class Solution {
public:
int calculate(string s) {
}
};
面试题 16.26. 计算器
给定一个包含正整数、加(+)、减(-)、乘(*)、除(/)的算数表达式(括号除外)，计算其结果。
表达式仅包含非负整数，+， - ，*，/ 四种运算符和空格 。 整数除法仅保留整数部分。
示例 1:
输入: "3+2*2" 输出: 7
示例 2:
输入: " 3/2 " 输出: 1
示例 3:
输入: " 3+5 / 2 " 输出: 5
说明：
eval。原站题解
java 解法, 执行用时: 14 ms, 内存消耗: 41.5 MB, 提交时间: 2022-11-30 23:28:15
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;
}
}
golang 解法, 执行用时: 4 ms, 内存消耗: 5.9 MB, 提交时间: 2022-11-30 23:27:58
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
}
javascript 解法, 执行用时: 108 ms, 内存消耗: 46.4 MB, 提交时间: 2022-11-30 23:27:43
/**
* @param {string} s
* @return {number}
*/
var calculate = function(s) {
s = s.trim();
const stack = [];
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;
};
python3 解法, 执行用时: 88 ms, 内存消耗: 59.4 MB, 提交时间: 2022-11-30 22:30:23
class Solution:
def calculate(self, s: str) -> int:
return eval(s.replace('/', '//'))