Given a string 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. 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 ~~~ ``` import java.util.Stack; class Solution { public boolean isValid(String s) { Stack<Character> stack = new Stack<>(); for(int i = 0 ; i < s.length() ; i ++){ char c = s.charAt(i); if(c == '(' || c == '[' || c == '{') stack.push(c); else{ if(stack.isEmpty()) return false; char topChar = stack.pop(); if(c == ')' && topChar != '(') return false; if(c == ']' && topChar != '[') return false; if(c == '}' && topChar != '{') return false; } } return stack.isEmpty(); } public static void main(String[] args) { System.out.println((new Solution()).isValid("()[]{}")); System.out.println((new Solution()).isValid("([)]")); } } ```