[20. 有效的括号](https://leetcode.cn/problems/valid-parentheses/)

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function(s) {
    if(s.length%2===1)return false;
    let stack=[];
    for(let i=0;i<s.length;i++){
        let c=s[i]
        if(c==='('||c==='['||c==='{'){
            stack.push(c);
        }else{
            let t=stack[stack.length-1]
            if((t==='('&&c===')')||(t==='['&&c===']')||(t==='{'&&c==='}')){
                stack.pop()
            }else{
                return false;
            }
        }
    }
    return stack.length===0;
};

use Map字典

var isValid = function(s) {
    if(s.length%2===1)return false;
    let stack=[];
    let map=new Map()
    map.set('(',')')
    map.set('[',']')
    map.set('{','}')
    for(let i=0;i<s.length;i++){
        let c=s[i]
        if(map.has(c)){
            stack.push(c);
        }else{
            let t=stack[stack.length-1]
            if(map.get(t)===c){
                stack.pop()
            }else{
                return false;
            }
        }
    }
    return stack.length===0;
};