LeetCode-in-Dart
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
class Solution {
bool isValid(String s) {
List<String> stack = [];
for (int i = 0; i < s.length; i++) {
String c = s[i];
if (c == '(' || c == '[' || c == '{') {
stack.add(c);
} else if (c == ')' && stack.isNotEmpty && stack.last == '(') {
stack.removeLast();
} else if (c == '}' && stack.isNotEmpty && stack.last == '{') {
stack.removeLast();
} else if (c == ']' && stack.isNotEmpty && stack.last == '[') {
stack.removeLast();
} else {
return false;
}
}
return stack.isEmpty;
}
}