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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.
经典老题，用stack。
一个个检查给的characters，如果是左括号都入栈；如果是右括号，检查栈如果为空，证明不能匹配，如果栈不空，弹出top，与当前扫描的括号检查是否匹配。
全部字符都检查完了以后，判断栈是否为空，空则正确都匹配，不空则证明有没匹配的。
注意：检查char是用==
Java code:
public boolean isValid(String s) { if(s.length() == 0) { return false; } Stack<Character> x = new Stack<Character>(); for(int i = 0; i < s.length(); i++) { if(s.charAt(i) ==‘(‘ || s.charAt(i) == ‘[‘ || s.charAt(i) == ‘{‘) { x.push(s.charAt(i)); }else{ if(x.size() == 0){ return false; } char y = s.charAt(i); char z = x.pop(); if(!((y == ‘)‘ && z == ‘(‘) || (y == ‘]‘ && z == ‘[‘) || (y == ‘}‘ && z == ‘{‘))){ return false; } } } return x.size() == 0; }
Reference:
1. http://www.cnblogs.com/springfor/p/3869420.html
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原文地址：http://www.cnblogs.com/anne-vista/p/4828548.html
