LeetCode-in-All
20. Valid Parentheses
Easy
Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:
- Open brackets must be closed by the same type of brackets.
- Open brackets must be closed in the correct order.
Example 1:
Input: s = “()”
Output: true
Example 2:
Input: s = “()[]{}”
Output: true
Example 3:
Input: s = “(]”
Output: false
Example 4:
Input: s = “([)]”
Output: false
Example 5:
Input: s = “{[]}”
Output: true
Constraints:
1 <= s.length <= 104sconsists of parentheses only'()[]{}'.
Solution
#include <stack>
#include <string>
using namespace std;
class Solution {
public:
bool isValid(string s) {
stack<char> stack;
for (char c : s) {
if (c == '(' || c == '[' || c == '{') {
stack.push(c);
} else if (c == ')' && !stack.empty() && stack.top() == '(') {
stack.pop();
} else if (c == '}' && !stack.empty() && stack.top() == '{') {
stack.pop();
} else if (c == ']' && !stack.empty() && stack.top() == '[') {
stack.pop();
} else {
return false;
}
}
return stack.empty();
}
};