有效的括号

js 版本

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function(s) {
    let stack = [];
    for(let i=0;i<s.length;i++) {
        let c = s[i];
        if(c === '(' || c === '[' || c === '{') {
            stack.push(c)
        }
        else {
            if(stack.length ===0 ) {
                return false;
            }
            let topChar = stack.pop();
              if(c === ')' && topChar != '(')
                    return false;
                if(c === ']' && topChar !== '[')
                    return false;
                if(c === '}' && topChar !== '{')
                    return false;
        }
    }
    if(stack.length == 0){
        return true
    }
    else{
        return false;
    }
};

java 版本

import java.util.Stack;

class Solution {

    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        for(int i = 0 ; i < s.length() ; i ++){
            char c = s.charAt(i);
            if(c == '(' || c == '[' || c == '{')
                stack.push(c);
            else{
                if(stack.isEmpty())
                    return false;

                char topChar = stack.pop();
                if(c == ')' && topChar != '(')
                    return false;
                if(c == ']' && topChar != '[')
                    return false;
                if(c == '}' && topChar != '{')
                    return false;
            }
        }
        return stack.isEmpty();
    }

    public static void main(String[] args) {

        System.out.println((new Solution()).isValid("()[]{}"));
        System.out.println((new Solution()).isValid("([)]"));
    }
}