Update validParentheses.java

Author: AyushJoshi2001

Topic/Solution/validParentheses.java

@@ -1,16 +1,64 @@
+/*
+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 <= 104
+s consists of parentheses only '()[]{}'.
+
+*/
+
+
+// funtional code
+
 class Solution {
      public boolean isValid(String s) {
          if (s.length() % 2 != 0) return false;
+          
+          // create a stack to store parentheses.
          Stack<Character> stack = new Stack<>();
          for (int i = 0; i < s.length(); i++) {
              char c = s.charAt(i);
+              // push opening parentheses.
              if (c == '(') {
                  stack.push(')');
              } else if (c == '[') {
                  stack.push(']');
              } else if (c == '{') {
                  stack.push('}');
-             } else if (stack.isEmpty() || stack.pop() != c) return false;
+             }
+              // check for coressponding closing parentheses if it is not there then return false.
+              else if (stack.isEmpty() || stack.pop() != c) return false;
          }
+          
+          // if the stack is empty that means parentheses are valid.
          return stack.isEmpty();
      }