20. Valid Parentheses
1. Description
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.
2. Example
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
3. Constraints
- 1 <= s.length <= $10^4$
- s consists of parentheses only ‘()[]{}’.
4. Solutions
My Accepted Solution
n = i_str.size()
Time complexity: O(n)
Space complexity: O(n)
class Solution {
public:
bool isValid(const string &str) {
stack<char> brackets;
for (char bracket : str) {
if (bracket == '(' || bracket == '[' || bracket == '{') {
brackets.push(bracket);
} else if (bracket == ')' && !brackets.empty() && brackets.top() == '(') {
brackets.pop();
} else if (bracket == ']' && !brackets.empty() && brackets.top() == '[') {
brackets.pop();
} else if (bracket == '}' && !brackets.empty() && brackets.top() == '{') {
brackets.pop();
} else {
return false;
}
}
return brackets.empty();
}
};