[路飞]_今夜简单栈操作

目标

1、化栈为队 leetcode-cn.com/problems/im…
2、球比赛 leetcode-cn.com/problems/ba…
3、较含退格的字符串 leetcode-cn.com/problems/ba…
4、证栈序列 leetcode-cn.com/problems/va…
5、除最外层的括号 leetcode-cn.com/problems/re…

化栈为队

class MyQueue {
  constructor() {
    this.left = []
    this.right = []
  }
  push(x) {
    this.left.push(x)
  }
  pop() {
    while (this.left.length) this.right.push(this.left.pop())
    const result = this.right.pop()
    while (this.right.length) this.left.push(this.right.pop())
    return result
  }
  peek() {
    return this.left[0]
  }
  empty() {
    return !this.left.length
  }
}
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球比赛

模拟解决，根据题目要求写代码即可

var calPoints = function(ops) {
    const len = ops.length;
    const list = [];
    for(let i = 0 ; i < len ; i++){
        if(ops[i] === 'C'){
            list.pop();
        }else if(ops[i] === 'D'){
            const l = list.length;
            list.push(list[l-1] * 2)
        }else if(ops[i] === '+'){
            const l = list.length;
             list.push(list[l-1] + list[l-2])
        }else{
            list.push(Number(ops[i]))
        }
    }
    //console.log('list',list)
    return list.reduce((a,b)=>a+b)

};
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较含退格的字符串

利用栈存储

遇到#删除数组最后一位即可

var backspaceCompare = function(s, t) {
    let a = [];
    for(let i = 0 ; i < s.length ; i++){
        if(s[i] === '#'){
            a.pop()
        }else{
            a.push(s[i])
        }
    }

     let b = [];
    for(let i = 0 ; i < t.length ; i++){
        if(t[i] === '#'){
            b.pop()
        }else{
            b.push(t[i])
        }
    }

    return a.join(',') === b.join(',')

};
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946. 验证栈序列

模拟法，一遍枚举过

var validateStackSequences = function(pushed, popped) {
    const list = [];
    const len = pushed.length;
    let idx = 0
    for(let i = 0 ; i < len ; i++){
        list.push(pushed[i]);
        while(list.length > 0 && list[list.length-1] === popped[idx]){
            idx++;
            list.pop();
        }

    }
    return list.length === 0
};
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1021. 删除最外层的括号

利用栈

使用变量将遇到的'('记录下来，超出1个"（"必然可以脱去最外城层（）

var removeOuterParentheses = function (s) {
  let num = 0
  let l = s.length
  let redult = ''
  for (let i = 0; i < l; i++) {
    if (s[i] == '(') {
      if (++num > 1) {
        redult += '('
      }
    } else {
      if (--num > 0) {
        redult += ')'
      }
    }
  }
  return redult
}

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