[LeetCode]20. Valid Parentheses

20. 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.

括号匹配的问题，用栈即可，左括号入栈，右括号则出栈比较是否匹配。最后记得检查栈是否为空。

class Solution {
public:
bool isValid(string s) {
stack<char> st;
for(int i = 0; i < s.size(); ++i){
char cur = s[i];
if(st.empty() || cur == '(' || cur == '{' || cur == '[')
st.push(cur);
else{
char top = st.top();
if(cur == ')' && top != '(')
return false;
if(cur == ']' && top != '[')
return false;
if(cur == '}' && top != '{')
return false;
st.pop();
}
}
if(st.empty())
return true;
return false;
}
};