From 79ceb6aac84ab374130dd0e51e654c443ad15c54 Mon Sep 17 00:00:00 2001
From: Raafat Akkad <RaafatAkkad@users.noreply.github.com>
Date: Mon, 6 Mar 2023 20:19:48 +0000
Subject: [PATCH] Optimize isValid implementation

* Set the HashMap initial capacity
* Strings and Boxed types should be compared using "equals()".
* Use String#charAt instead of String#toCharArray to avoid using O(n) space
* Simplify return statement
---
 java/0020-valid-parentheses.java | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/java/0020-valid-parentheses.java b/java/0020-valid-parentheses.java
index 5d54eb195..d41194111 100644
--- a/java/0020-valid-parentheses.java
+++ b/java/0020-valid-parentheses.java
@@ -28,15 +28,16 @@ public boolean isValid(String s) {
 class Solution {
     public boolean isValid(String s) {
         Stack<Character> brackets = new Stack<>();
-        Map<Character, Character> bracketLookup = new HashMap<>();
+        Map<Character, Character> bracketLookup = new HashMap<>(3);
 
         bracketLookup.put(')', '(');
         bracketLookup.put('}', '{');
         bracketLookup.put(']', '[');
 
-        for (char c : s.toCharArray()) {
+        for (int i = 0; i < s.length(); i++) {
+            char c = s.charAt(i);
             if (bracketLookup.containsKey(c)) {
-                if (brackets.size() != 0 && brackets.peek() == bracketLookup.get(c)) {
+                if (!brackets.isEmpty() && bracketLookup.get(c).equals(brackets.peek())) {
                     brackets.pop();
                 } else {
                     return false;
@@ -46,7 +47,6 @@ public boolean isValid(String s) {
             }
         }
 
-        if (brackets.size() == 0) return true;
-        return false;
+        return brackets.isEmpty();
     }
 }