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Harshil bhardwaj
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Merge pull request #58 from Pranit5895/master
Solutions
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‎22Day22/SOL/N-Queens.java

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/* Java program to solve N Queen Problem using
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backtracking */
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public class NQueenProblem {
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final int N = 4;
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/* A utility function to print solution */
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void printSolution(int board[][])
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{
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for (int i = 0; i < N; i++) {
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for (int j = 0; j < N; j++)
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System.out.print(" " + board[i][j]
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+ " ");
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System.out.println();
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}
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}
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/* A utility function to check if a queen can
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be placed on board[row][col]. Note that this
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function is called when "col" queens are already
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placeed in columns from 0 to col -1. So we need
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to check only left side for attacking queens */
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boolean isSafe(int board[][], int row, int col)
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{
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int i, j;
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/* Check this row on left side */
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for (i = 0; i < col; i++)
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if (board[row][i] == 1)
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return false;
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/* Check upper diagonal on left side */
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for (i = row, j = col; i >= 0 && j >= 0; i--, j--)
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if (board[i][j] == 1)
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return false;
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/* Check lower diagonal on left side */
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for (i = row, j = col; j >= 0 && i < N; i++, j--)
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if (board[i][j] == 1)
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return false;
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return true;
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}
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/* A recursive utility function to solve N
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Queen problem */
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boolean solveNQUtil(int board[][], int col)
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{
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/* base case: If all queens are placed
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then return true */
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if (col >= N)
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return true;
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/* Consider this column and try placing
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this queen in all rows one by one */
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for (int i = 0; i < N; i++) {
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/* Check if the queen can be placed on
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board[i][col] */
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if (isSafe(board, i, col)) {
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/* Place this queen in board[i][col] */
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board[i][col] = 1;
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/* recur to place rest of the queens */
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if (solveNQUtil(board, col + 1) == true)
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return true;
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/* If placing queen in board[i][col]
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doesn't lead to a solution then
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remove queen from board[i][col] */
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board[i][col] = 0; // BACKTRACK
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}
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}
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/* If the queen can not be placed in any row in
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this colum col, then return false */
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return false;
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}
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/* This function solves the N Queen problem using
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Backtracking. It mainly uses solveNQUtil () to
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solve the problem. It returns false if queens
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cannot be placed, otherwise, return true and
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prints placement of queens in the form of 1s.
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Please note that there may be more than one
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solutions, this function prints one of the
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feasible solutions.*/
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boolean solveNQ()
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{
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int board[][] = { { 0, 0, 0, 0 },
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{ 0, 0, 0, 0 },
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{ 0, 0, 0, 0 },
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{ 0, 0, 0, 0 } };
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if (solveNQUtil(board, 0) == false) {
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System.out.print("Solution does not exist");
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return false;
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}
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printSolution(board);
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return true;
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}
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// driver program to test above function
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public static void main(String args[])
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{
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NQueenProblem Queen = new NQueenProblem();
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Queen.solveNQ();
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}
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}

‎24Day24/SOL/8-Queens.java

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// This program solves the classic "8 queens" problem using recursive
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// backtracking.
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import java.util.*;
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public class Queens {
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public static void main(String[] args) {
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giveIntro();
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Scanner console = new Scanner(System.in);
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System.out.print("What size board do you want to use? ");
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int size = console.nextInt();
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System.out.println();
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Board b = new Board(size);
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solve(b);
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}
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// post: explains program to user
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public static void giveIntro() {
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System.out.println("This program solves the classic '8 queens'");
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System.out.println("problem, placing queens on a chessboard so");
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System.out.println("that no two queens threaten each other.");
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System.out.println();
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}
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// pre : queens have been safely placed in columns 1 through (col - 1)
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// post: recursively searchs the board for a solution starting at col,
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// returning true iff such a solution occurs and storing the
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// solution in board if it exists
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public static boolean explore(Board b, int col) {
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if (col > b.size())
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return true;
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else {
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for (int row = 1; row <= b.size(); row++)
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if (b.safe(row, col)) {
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b.place(row, col);
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for (int i = 1; i < col; i++)
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System.out.print(" ");
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System.out.println("Q in row " + row + " of col " + col);
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if (explore(b, col + 1))
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return true;
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b.remove(row, col);
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}
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return false;
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}
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}
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// post: searches for a solution to the 8 queens problem with this
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// board, reporting result.
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public static void solve(Board solution) {
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if (!explore(solution, 1))
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System.out.println("No solution.");
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else {
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System.out.println("One solution is as follows:");
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solution.print();
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}
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}
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}

‎28Day28/SOL/Solution.java

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// Java program to create a simple calculator
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// with basic +, -, /, * using java swing elements
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import java.awt.event.*;
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import javax.swing.*;
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import java.awt.*;
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class calculator extends JFrame implements ActionListener {
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// create a frame
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static JFrame f;
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// create a textfield
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static JTextField l;
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// store oprerator and operands
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String s0, s1, s2;
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// default constrcutor
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calculator()
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{
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s0 = s1 = s2 = "";
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}
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// main function
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public static void main(String args[])
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{
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// create a frame
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f = new JFrame("calculator");
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try {
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// set look and feel
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UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
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}
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catch (Exception e) {
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System.err.println(e.getMessage());
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}
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// create a object of class
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calculator c = new calculator();
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// create a textfield
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l = new JTextField(16);
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// set the textfield to non editable
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l.setEditable(false);
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// create number buttons and some operators
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JButton b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bs, bd, bm, be, beq, beq1;
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// create number buttons
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b0 = new JButton("0");
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b1 = new JButton("1");
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b2 = new JButton("2");
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b3 = new JButton("3");
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b4 = new JButton("4");
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b5 = new JButton("5");
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b6 = new JButton("6");
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b7 = new JButton("7");
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b8 = new JButton("8");
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b9 = new JButton("9");
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// equals button
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beq1 = new JButton("=");
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// create operator buttons
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ba = new JButton("+");
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bs = new JButton("-");
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bd = new JButton("/");
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bm = new JButton("*");
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beq = new JButton("C");
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// create . button
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be = new JButton(".");
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// create a panel
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JPanel p = new JPanel();
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// add action listeners
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bm.addActionListener(c);
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bd.addActionListener(c);
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bs.addActionListener(c);
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ba.addActionListener(c);
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b9.addActionListener(c);
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b8.addActionListener(c);
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b7.addActionListener(c);
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b6.addActionListener(c);
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b5.addActionListener(c);
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b4.addActionListener(c);
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b3.addActionListener(c);
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b2.addActionListener(c);
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b1.addActionListener(c);
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b0.addActionListener(c);
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be.addActionListener(c);
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beq.addActionListener(c);
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beq1.addActionListener(c);
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// add elements to panel
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p.add(l);
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p.add(ba);
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p.add(b1);
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p.add(b2);
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p.add(b3);
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p.add(bs);
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p.add(b4);
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p.add(b5);
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p.add(b6);
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p.add(bm);
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p.add(b7);
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p.add(b8);
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p.add(b9);
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p.add(bd);
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p.add(be);
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p.add(b0);
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p.add(beq);
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p.add(beq1);
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// set Background of panel
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p.setBackground(Color.blue);
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// add panel to frame
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f.add(p);
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f.setSize(200, 220);
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f.show();
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}
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public void actionPerformed(ActionEvent e)
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{
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String s = e.getActionCommand();
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// if the value is a number
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if ((s.charAt(0) >= '0' && s.charAt(0) <= '9') || s.charAt(0) == '.') {
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// if operand is present then add to second no
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if (!s1.equals(""))
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s2 = s2 + s;
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else
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s0 = s0 + s;
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// set the value of text
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l.setText(s0 + s1 + s2);
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}
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else if (s.charAt(0) == 'C') {
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// clear the one letter
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s0 = s1 = s2 = "";
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// set the value of text
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l.setText(s0 + s1 + s2);
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}
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else if (s.charAt(0) == '=') {
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double te;
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// store the value in 1st
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if (s1.equals("+"))
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te = (Double.parseDouble(s0) + Double.parseDouble(s2));
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else if (s1.equals("-"))
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te = (Double.parseDouble(s0) - Double.parseDouble(s2));
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else if (s1.equals("/"))
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te = (Double.parseDouble(s0) / Double.parseDouble(s2));
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else
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te = (Double.parseDouble(s0) * Double.parseDouble(s2));
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// set the value of text
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l.setText(s0 + s1 + s2 + "=" + te);
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// convert it to string
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s0 = Double.toString(te);
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s1 = s2 = "";
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}
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else {
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// if there was no operand
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if (s1.equals("") || s2.equals(""))
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s1 = s;
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// else evaluate
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else {
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double te;
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// store the value in 1st
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if (s1.equals("+"))
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te = (Double.parseDouble(s0) + Double.parseDouble(s2));
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else if (s1.equals("-"))
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te = (Double.parseDouble(s0) - Double.parseDouble(s2));
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else if (s1.equals("/"))
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te = (Double.parseDouble(s0) / Double.parseDouble(s2));
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else
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te = (Double.parseDouble(s0) * Double.parseDouble(s2));
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// convert it to string
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s0 = Double.toString(te);
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// place the operator
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s1 = s;
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// make the operand blank
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s2 = "";
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}
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// set the value of text
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l.setText(s0 + s1 + s2);
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}
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}
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}

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