【LeetCode】20.Valid Parentheses（有效的括号）

Jim-2ha02024-07-02 12:17

描述

Given a string s containing just the characters '(', ')', '{', '}', ' $' and '$ ', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.

Open brackets must be closed in the correct order.

Every close bracket has a corresponding open bracket of the same type.

例子

text 复制代码

Example 1:

Input: s = "()"
Output: true
Example 2:

Input: s = "()[]{}"
Output: true
Example 3:

Input: s = "(]"
Output: false

约束 Constraints:

1 <= s.length <= 104
s consists of parentheses only ()[]{}.

JS实现

javascript 复制代码

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function(s) {
    let stack = [];
    const pairs = {'}':'{',']':'[',')':'('}
    for(let c of s){
        if( !pairs[c] ){
        	// 碰到左括号压栈
            stack.push(c) 
        }else if( !stack.length || stack.pop() != pairs[c]){
            // 如果碰到右括号找不到左括号（包含 栈为空 场景）则说明输入S不是有效括号
            return false
        }
    }
    // 根据栈内是否还存在左括号判断 输入S 是否有效的括号
    return !stack.length
};