LeetCode 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.

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