c 解法, 执行用时: 4 ms, 内存消耗: 8.3 MB, 提交时间: 2023-09-07 10:45:38

int calculate(char* s) {
    int n = strlen(s);
    int stk[n], top = 0;
    char preSign = '+';
    int num = 0;
    for (int i = 0; i < n; ++i) {
        if (isdigit(s[i])) {
            num = num * 10 + (int)(s[i] - '0');
        }
        if (!isdigit(s[i]) && s[i] != ' ' || i == n - 1) {
            switch (preSign) {
                case '+':
                    stk[top++] = num;
                    break;
                case '-':
                    stk[top++] = -num;
                    break;
                case '*':
                    stk[top - 1] *= num;
                    break;
                default:
                    stk[top - 1] /= num;
            }
            preSign = s[i];
            num = 0;
        }
    }
    int ret = 0;
    for (int i = 0; i < top; i++) {
        ret += stk[i];
    }
    return ret;
}

cpp 解法, 执行用时: 8 ms, 内存消耗: 12.3 MB, 提交时间: 2023-09-07 10:45:18

class Solution {
public:
    int calculate(string s) {
        vector<int> stk;
        char preSign = '+';
        int num = 0;
        int n = s.length();
        for (int i = 0; i < n; ++i) {
            if (isdigit(s[i])) {
                num = num * 10 + int(s[i] - '0');
            }
            if (!isdigit(s[i]) && s[i] != ' ' || i == n - 1) {
                switch (preSign) {
                    case '+':
                        stk.push_back(num);
                        break;
                    case '-':
                        stk.push_back(-num);
                        break;
                    case '*':
                        stk.back() *= num;
                        break;
                    default:
                        stk.back() /= num;
                }
                preSign = s[i];
                num = 0;
            }
        }
        return accumulate(stk.begin(), stk.end(), 0);
    }
};

java 解法, 执行用时: 18 ms, 内存消耗: 43.9 MB, 提交时间: 2023-09-07 10:45:00

class Solution {
    public int calculate(String s) {
        Deque<Integer> stack = new ArrayDeque<Integer>();
        char preSign = '+';
        int num = 0;
        int n = s.length();
        for (int i = 0; i < n; ++i) {
            if (Character.isDigit(s.charAt(i))) {
                num = num * 10 + s.charAt(i) - '0';
            }
            if (!Character.isDigit(s.charAt(i)) && s.charAt(i) != ' ' || i == n - 1) {
                switch (preSign) {
                case '+':
                    stack.push(num);
                    break;
                case '-':
                    stack.push(-num);
                    break;
                case '*':
                    stack.push(stack.pop() * num);
                    break;
                default:
                    stack.push(stack.pop() / num);
                }
                preSign = s.charAt(i);
                num = 0;
            }
        }
        int ans = 0;
        while (!stack.isEmpty()) {
            ans += stack.pop();
        }
        return ans;
    }
}

javascript 解法, 执行用时: 96 ms, 内存消耗: 50.2 MB, 提交时间: 2023-09-07 10:44:34

/**
 * @param {string} s
 * @return {number}
 */
var calculate = function(s) {
    s = s.trim();
    const stack = new Array();
    let preSign = '+';
    let num = 0;
    const n = s.length;
    for (let i = 0; i < n; ++i) {
        if (!isNaN(Number(s[i])) && s[i] !== ' ') {
            num = num * 10 + s[i].charCodeAt() - '0'.charCodeAt();
        }
        if (isNaN(Number(s[i])) || i === n - 1) {
            switch (preSign) {
                case '+':
                    stack.push(num);
                    break;
                case '-':
                    stack.push(-num);
                    break;
                case '*':
                    stack.push(stack.pop() * num);
                    break;
                default:
                    stack.push(stack.pop() / num | 0);
            }   
            preSign = s[i];
            num = 0;
        }
    }
    let ans = 0;
    while (stack.length) {
        ans += stack.pop();
    }
    return ans;
};

golang 解法, 执行用时: 0 ms, 内存消耗: 8.4 MB, 提交时间: 2023-09-07 10:44:12

func calculate(s string) (ans int) {
    stack := []int{}
    preSign := '+'
    num := 0
    for i, ch := range s {
        isDigit := '0' <= ch && ch <= '9'
        if isDigit {
            num = num*10 + int(ch-'0')
        }
        if !isDigit && ch != ' ' || i == len(s)-1 {
            switch preSign {
            case '+':
                stack = append(stack, num)
            case '-':
                stack = append(stack, -num)
            case '*':
                stack[len(stack)-1] *= num
            default:
                stack[len(stack)-1] /= num
            }
            preSign = ch
            num = 0
        }
    }
    for _, v := range stack {
        ans += v
    }
    return
}

python3 解法, 执行用时: 148 ms, 内存消耗: 19.6 MB, 提交时间: 2023-09-07 10:43:41

# 用栈来处理
class Solution:
    def calculate(self, s: str) -> int:
        n = len(s)
        stack = []
        preSign = '+'
        num = 0
        for i in range(n):
            if s[i] != ' ' and s[i].isdigit():
                num = num * 10 + ord(s[i]) - ord('0')
            if i == n - 1 or s[i] in '+-*/':
                if preSign == '+':
                    stack.append(num)
                elif preSign == '-':
                    stack.append(-num)
                elif preSign == '*':
                    stack.append(stack.pop() * num)
                else:
                    stack.append(int(stack.pop() / num))
                preSign = s[i]
                num = 0
        return sum(stack)