Difficulty: Easy
Given a string 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.
Note that an empty string is also considered valid.
Example 1:
Input: "()"
Output: true
Example 2:
Input: "()[]{}"
Output: true
Example 3:
Input: "(]"
Output: false
Example 4:
Input: "([)]"
Output: false
Example 5:
Input: "{[]}"
Output: true
Language: Java
class Solution {
public boolean isValid(String s) {
List<Character> left = Arrays.asList('(', '{', '[');
List<Character> right = Arrays.asList(')', '}', ']');
Stack<Integer> stack = new Stack<>();
for (char c : s.toCharArray()) {
if (left.contains(c)) {
stack.push(left.indexOf(c));
} else if (right.contains(c)) {
if (stack.empty() || !stack.pop().equals(right.indexOf(c))) {
return false;
}
} else {
return false;
}
}
return stack.empty();
}
}