LeetCode 20.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.
分析与解答：
利用栈的原理，当遇到左边括号时将其进栈。遇到右边括号时，栈为空就输出false，接着判断栈顶元素是否与其相匹配，匹配就弹出栈顶元素。不匹配就输出false。其实string的长度是奇数就可以判断为false了。

class Solution {
public:
bool isValid(string s) {
int size = s.size();
if (size == 0)
return 1;
if (size % 2)
return 0;
vector<char> v;
v.clear();
for (int i = 0; i < size; i++) {
if (s[i] == ')' || s[i] == ']' || s[i] == '}') {
if (v.empty() || (s[i] == ')' && v.back() != '(')
|| (s[i] == ']' && v.back() != '[')
|| (s[i] == '}' && v.back() != '{')) {
return 0;
} else
v.pop_back();
} else {
v.push_back(s[i]);
}
}
return v.empty();
}
};