4.1.1 Valid Parentheses

原题链接：https://oj.leetcode.com/problems/valid-parentheses/

这题简单。一次过。

public class Solution {    public boolean isValid(String s) {        Stack<Character> stack = new Stack<Character>();        char c;        for(int i = 0; i < s.length(); i++){            c = s.charAt(i);            if(c == '(' || c == '[' || c == '{'){                stack.push(c);            }            else if (c == ')' || c == ']' || c == '}'){            //dont forget this: there are more right parenthese                if(stack.size() == 0)  return false;                char d = stack.peek();                if(c==')' && d!='(') return false;                if(c==']' && d!='[') return false;                if(c=='}' && d!='{') return false;                else stack.pop();            }        }        //return true;        return stack.size() == 0;    }}