Update 20_Valid_Parentheses.java

Author: seanprashad

Stacks/20_Valid_Parentheses.java

@@ -1,27 +1,25 @@
 class Solution {
-    public static boolean isValid(String s) {
+    public boolean isValid(String s) {
         if (s == null || s.length() == 0) {
             return true;
         }
 
-        Stack<Character> st = new Stack<Character>();
+        Stack<Character> st = new Stack<>();
 
-        for (Character c : s.toCharArray()) {
+        for (char c : s.toCharArray()) {
             if (c == '(') {
                 st.push(')');
             } else if (c == '{') {
                 st.push('}');
             } else if (c == '[') {
                 st.push(']');
-            } else if (st.empty() || st.pop() != c) {
+            } else if (st.isEmpty() || c != st.peek()) {
                 return false;
+            } else {
+                st.pop();
             }
         }
 
-        if (!st.empty()) {
-            return false;
-        }
-
-        return true;
+        return st.isEmpty();
     }
 }