Create Solution.cpp

Author: yanglbme

solution/0700-0799/0772.Basic Calculator III/Solution.cpp

@@ -0,0 +1,127 @@
+#include <stack>
+#include <string>
+using namespace std;
+
+class Solution {
+public:
+    // Define an operation function that performs mathematical operations based on the operator
+    int operate(int b, char ch, int a) {
+        // Note the order of ab
+        switch (ch) {
+        case '+':
+            return a + b; // Addition
+        case '-':
+            return a - b; // Subtraction
+        case '*':
+            return a * b; // Multiplication
+        case '/':
+            return a / b; // Division
+        default:
+            break;
+        }
+        return 0; // Default return 0, handle invalid operators
+    }
+
+    // Calculate the value of the string expression
+    int calculate(string s) {
+        int preority[250]; // Operator precedence array
+        preority['+'] = 1;
+        preority['-'] = 1;
+        preority['*'] = 2;
+        preority['/'] = 2;
+        preority['('] = 0;
+        preority[')'] = 0;
+
+        stack<char> op; // Operator stack
+        stack<int> num; // Operand stack
+        int stringsize = s.size(); // Length of the string
+        int i = 0;
+        char ch;
+
+        // Traverse the string
+        for (; i < stringsize; i++) {
+            ch = s[i];
+            if (ch == ' ') {
+                continue; // Skip spaces
+            }
+            if (ch >= '0' && ch <= '9') {
+                int realnum = ch - '0'; // Convert character to number
+                // Handle multi-digit numbers
+                while (s[i + 1] >= '0' && s[i + 1] <= '9') {
+                    i++;
+                    realnum *= 10;
+                    realnum += s[i] - '0';
+                }
+                num.push(realnum); // Push the number onto the stack
+            } else {
+                // Handle operators
+                if (op.empty() || ch == '(' || preority[ch] > preority[op.top()]) {
+                    // Special case, handle the first character being '-' or '+'
+                    if (num.empty() && (ch == '-' || ch == '+')) {
+                        num.push(0);
+                    }
+                    op.push(ch); // Push the operator onto the stack
+                    // Handle expressions inside parentheses
+                    if (ch == '(') {
+                        int j = i;
+                        while (j + 1 < stringsize) {
+                            // Preprocess the first operator inside the parentheses
+                            if (s[j + 1] == '-' || s[j + 1] == '+') {
+                                num.push(0);
+                            }
+                            if (s[j + 1] != ' ') {
+                                break;
+                            }
+                            j++;
+                        }
+                    }
+                } else if (ch == ')') {
+                    // Handle right parentheses
+                    char ch2 = ')';
+                    ch2 = op.top();
+                    op.pop();
+                    while (ch2 != '(') {
+                        int a = num.top();
+                        num.pop();
+                        int b = num.top();
+                        num.pop();
+                        num.push(operate(a, ch2, b)); // Calculate and push the result
+                        ch2 = op.top();
+                        op.pop();
+                    }
+                } else if (preority[ch] <= preority[op.top()]) {
+                    // Handle cases where the precedence is less than or equal to the top of the stack
+                    char ch2;
+                    ch2 = op.top();
+                    while (!op.empty() && preority[ch] <= preority[op.top()] && ch2 != '(') {
+                        op.pop();
+                        int a = num.top();
+                        num.pop();
+                        int b = num.top();
+                        num.pop();
+                        num.push(operate(a, ch2, b)); // Calculate and push the result
+                        if (!op.empty()) {
+                            ch2 = op.top();
+                        } else {
+                            break;
+                        }
+                    }
+                    op.push(ch); // Push the current operator onto the stack
+                }
+            }
+        }
+
+        // Handle the remaining expressions in the stack
+        while (!op.empty()) {
+            ch = op.top();
+            op.pop();
+            int a = num.top();
+            num.pop();
+            int b = num.top();
+            num.pop();
+            num.push(operate(a, ch, b)); // Calculate and push the result
+        }
+
+        return num.top(); // Return the final result
+    }
+};