Valid Parentheses

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.
3. Every close bracket has a corresponding open bracket of the same type.

 

Example 1:

Input: s = "()"

Output: true

Example 2:

Input: s = "()[]{}"

Output: true

Example 3:

Input: s = "(]"

Output: false

Example 4:

Input: s = "([])"

Output: true

Solution

class Solution {

public boolean isValid(String s) {

Stack<Character> stack = new Stack<Character>();

for(Character c: s.toCharArray()){

if(c == '(') {

stack.push(')');

} else if(c == '{') {

stack.push('}');

} else if(c == '[') {

stack.push(']');

} else if(stack.isEmpty() || stack.pop() != c){

return false;

}

}

return stack.isEmpty();

}

}