Create n_queen.cpp

Author: Abhinavcode13

Backtracking/n_queen.cpp

@@ -0,0 +1,80 @@
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+// Function to check if it's safe to place a queen at board[row][col]
+bool isSafe(vector<string>& board, int row, int col, int N) {
+    // Check the row on the left side
+    for (int i = 0; i < col; ++i) {
+        if (board[row][i] == 'Q') {
+            return false;
+        }
+    }
+
+    // Check upper diagonal on the left side
+    for (int i = row, j = col; i >= 0 && j >= 0; --i, --j) {
+        if (board[i][j] == 'Q') {
+            return false;
+        }
+    }
+
+    // Check lower diagonal on the left side
+    for (int i = row, j = col; i < N && j >= 0; ++i, --j) {
+        if (board[i][j] == 'Q') {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+// Recursive function to solve N-Queens problem
+bool solveNQueens(vector<string>& board, int col, int N) {
+    if (col == N) {
+        // All queens are placed successfully
+        return true;
+    }
+
+    for (int i = 0; i < N; ++i) {
+        if (isSafe(board, i, col, N)) {
+            // Place queen
+            board[i][col] = 'Q';
+
+            // Recur to place the rest of the queens
+            if (solveNQueens(board, col + 1, N)) {
+                return true;
+            }
+
+            // If placing queen in board[i][col] doesn't lead to a solution, backtrack
+            board[i][col] = '.';
+        }
+    }
+
+    // If no queen can be placed in this column, return false
+    return false;
+}
+
+// Function to solve N-Queens problem and print the solution
+void solveNQueens(int N) {
+    vector<string> board(N, string(N, '.'));
+
+    if (solveNQueens(board, 0, N)) {
+        // Print the solution
+        for (int i = 0; i < N; ++i) {
+            cout << board[i] << endl;
+        }
+    } else {
+        cout << "No solution exists." << endl;
+    }
+}
+
+int main() {
+    int N;
+    cout << "Enter the number of queens (N): ";
+    cin >> N;
+
+    solveNQueens(N);
+
+    return 0;
+}