🧮 Day 24

Author: Akash Rajpurohit

README.md

@@ -34,6 +34,7 @@
 ## Week 4 🚧
 1. [Unique Morse Code Words](https://leetcode.com/explore/challenge/card/november-leetcoding-challenge/567/week-4-november-22nd-november-28th/3540/) ➡️ [CPP Solution](Week4/uniqueMorseRepresentations.cpp)
 2. [House Robber III](https://leetcode.com/explore/challenge/card/november-leetcoding-challenge/567/week-4-november-22nd-november-28th/3541/) ➡️ [CPP Solution](Week4/rob.cpp)
+3. [Basic Calculator II](https://leetcode.com/explore/challenge/card/november-leetcoding-challenge/567/week-4-november-22nd-november-28th/3542/) ➡️ [CPP Solution](Week4/calculate.cpp)
 
 ## Week 5 🚧
 Coming soon...

Week4/calculate.cpp

@@ -0,0 +1,65 @@
+class Solution {
+private:
+    int getPrecedence(char op) {
+        if(op == '*' || op == '/') 
+            return 1;
+        
+        return 0;
+    }
+    
+    int performOperation(char op, int op1, int op2) {
+        switch(op) {
+            case '*':
+                return op1 * op2;
+            case '/':
+                return op1 / op2;
+            case '+':
+                return op1 + op2;
+            case '-':
+                return op1 - op2;
+            default:
+                return 0;
+        }
+    }
+public:
+    int calculate(string s) {
+        stack<int> operandStack;
+        stack<char> operatorStack;
+        int n = s.size();
+        
+        for(int i = 0; i < n; ++i) {
+            if(isdigit(s[i])) {
+                int num = 0;
+                while(i < n && isdigit(s[i])) {
+                    num *= 10;
+                    num += s[i] - '0';
+                    i++;
+                }
+                i--;
+                operandStack.push(num);
+            } else if(s[i] != ' ') {
+                int chPrecedence = getPrecedence(s[i]);
+                
+                while(!operatorStack.empty() && chPrecedence <= getPrecedence(operatorStack.top())) {
+                    char op = operatorStack.top(); operatorStack.pop();
+                    int op2 = operandStack.top(); operandStack.pop();
+                    int op1 = operandStack.top(); operandStack.pop();
+                    
+                    operandStack.push(performOperation(op, op1, op2));
+                }
+                
+                operatorStack.push(s[i]);
+            }
+        }
+        
+        while(!operatorStack.empty()) {
+            char op = operatorStack.top(); operatorStack.pop();
+            int op2 = operandStack.top(); operandStack.pop();
+            int op1 = operandStack.top(); operandStack.pop();
+
+            operandStack.push(performOperation(op, op1, op2));
+        }
+        
+        return operandStack.top();
+    }
+};