added Valid Parentheses Solution

Author: AyushJoshi2001

Topic/Solution/validParentheses.java

@@ -0,0 +1,16 @@
+class Solution {
+     public boolean isValid(String s) {
+         if (s.length() % 2 != 0) return false;
+         Stack<Character> stack = new Stack<>();
+         for (int i = 0; i < s.length(); i++) {
+             char c = s.charAt(i);
+             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();
+     }