Leetcode Valid Parentheses

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.

解题思路：

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