fix: change Deque to Stack for readability and familiarity of using Stack

Author: Jer3myYu

java/Stacks/ImplementAQueueUsingAStack.java

@@ -1,13 +1,12 @@
-import java.util.ArrayDeque;
-import java.util.Deque;
+import java.util.Stack;
 
 public class ImplementAQueueUsingAStack {
-    Deque<Integer> enqueueStack;
-    Deque<Integer> dequeueStack;
+    Stack<Integer> enqueueStack;
+    Stack<Integer> dequeueStack;
 
     public ImplementAQueueUsingAStack() {
-        this.enqueueStack = new ArrayDeque<>();
-        this.dequeueStack = new ArrayDeque<>();
+        this.enqueueStack = new Stack<>();
+        this.dequeueStack = new Stack<>();
     }
 
     public void enqueue(int x) {

java/Stacks/NextLargestNumberToTheRight.java

@@ -1,10 +1,9 @@
-import java.util.ArrayDeque;
-import java.util.Deque;
+import java.util.Stack;
 
 public class NextLargestNumberToTheRight {
     public int[] nextLargestNumberToTheRight(int[] nums) {
         int[] res = new int[nums.length];
-        Deque<Integer> stack = new ArrayDeque<>();
+        Stack<Integer> stack = new Stack<>();
         // Find the next largest number of each element, starting with the 
         // rightmost element.
         for (int i = nums.length - 1; i >= 0; i--) {

java/Stacks/ValidParenthesisExpression.java

@@ -1,13 +1,11 @@
-import java.util.ArrayDeque;
-import java.util.Deque;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Stack;
 
 public class ValidParenthesisExpression {
     public boolean validParenthesisExpression(String s) {
         Map<Character, Character> parenthesesMap = new HashMap<>();
-        Deque<Character> stack = new ArrayDeque<>();
+        Stack<Character> stack = new Stack<>();
         parenthesesMap.put('(', ')');
         parenthesesMap.put('{', '}');
         parenthesesMap.put('[', ']');