227.基本计算器II

链接：227.基本计算器II
难度：Medium
标签：栈、数学、字符串
简介：给你一个字符串表达式 s ，请你实现一个基本计算器来计算并返回它的值。

题解 1 - typescript

• 编辑时间：2021-03-11
• 执行用时：148ms
• 内存消耗：50.6MB
• 编程语言：typescript
• 解法介绍：先乘除后加减。

const numReg = /\-?\d+/;
const opMap: Record<string, (num1: number, num2: number) => number> = {
  '+': (num1, num2) => num1 + num2,
  '-': (num1, num2) => num1 - num2,
  '*': (num1, num2) => num1 * num2,
  '/': (num1, num2) => ~~(num1 / num2),
};
function calculate(s: string): number {
  s = s.replace(/ /g, '');
  const len = s.length;
  const stack: string[] = [];
  const peek = () => stack[stack.length - 1];
  // 去乘除
  for (let i = 0; i < len; i++) {
    let c = s[i];
    if (c === '*' || c === '/' || c === '+') {
      stack.push(c);
    } else if (c === '-') {
      if (stack.length === 0) stack.push('0');
      stack.push(c);
    } else {
      while (i < len - 1 && numReg.test(s[i + 1])) {
        c += s[i + 1];
        i++;
      }
      const top = peek();
      if (stack.length === 0) {
        stack.push(c);
      } else if (top === '*' || top === '/') {
        const op = stack.pop()!;
        const num1 = +stack.pop()!;
        const num2 = +c;
        stack.push(opMap[op](num1, num2) + '');
      } else if (top === '-') {
        stack[stack.length - 1] = '+';
        stack.push(c.startsWith('-') ? c.substr(1) : '-' + c);
      } else {
        stack.push(c);
      }
    }
  }
  // 去加减
  const newStack: string[] = [];
  for (const c of stack) {
    if (numReg.test(c)) {
      if (newStack[newStack.length - 1] === '+') {
        const op = newStack.pop()!;
        const num1 = +newStack.pop()!;
        const num2 = +c;
        newStack.push(opMap[op](num1, num2) + '');
      } else {
        newStack.push(c);
      }
    } else {
      newStack.push(c);
    }
  }
  return +newStack[0];
}