【Leetcode】Valid Parentheses

题目链接：https://leetcode.com/problems/valid-parentheses/

题目：

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

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

思路：

用栈，easy。。

算法：

 public boolean isMatch(char c1, char c2) {
     if (c1 == '(' && c2 == ')')
         return true;
     if (c1 == '[' && c2 == ']')
         return true;
     if (c1 == '{' && c2 == '}')
         return true;
     return false;
 }

 public boolean isValid(String s) {
     Stack<Character> stk = new Stack<Character>();
     char c[] = s.toCharArray();
     for (char i : c) {
         if (!stk.isEmpty()) {
             char t = (char) stk.pop();
             if (!isMatch(t, i)) {// 如果可以抵消
                 stk.push(t);
                 stk.push(i);
             }
         } else {
             stk.push(i);
         }
     }
     if (!stk.isEmpty())
         return false;
     else
         return true;
 }