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

Author: Jer3myYu

java/Stacks/EvaluateExpression.java

@@ -1,9 +1,8 @@
-import java.util.ArrayDeque;
-import java.util.Deque;
+import java.util.Stack;
 
 public class EvaluateExpression {
     public int evaluateExpression(String s) {
-        Deque<Integer> stack = new ArrayDeque<>();
+        Stack<Integer> stack = new Stack<>();  
         int currNum = 0;
         int sign = 1;
         int res = 0;

java/Stacks/MaximumsOfSlidingWindow.java

@@ -1,29 +1,28 @@
-import java.util.ArrayDeque;
-import java.util.Deque;
+import java.util.Stack;
 
 public class MaximumsOfSlidingWindow {
     public int[] maximumsOfSlidingWindow(int[] nums, int k) {
         int[] res = new int[nums.length - k + 1];
-        Deque<int[]> dq = new ArrayDeque<>();
+        Stack<int[]> dq = new Stack<>();
         int left, right;
         left = right = 0;
         while (right < nums.length) {
             // 1) Ensure the values of the deque maintain a monotonic decreasing order
             // by removing candidates <= the current candidate.
-            while (!dq.isEmpty() && dq.peekLast()[0] <= nums[right]) {
-                dq.pollLast();
+            while (!dq.isEmpty() && dq.peek()[0] <= nums[right]) {
+                dq.pop();
             }
             // 2) Add the current candidate.
-            dq.offerLast(new int[]{nums[right], right});
+            dq.push(new int[]{nums[right], right});
             // If the window is of length 'k', record the maximum of the window.
             if (right - left + 1 == k) {
                 // 3) Remove values whose indexes occur outside the window.
-                if (!dq.isEmpty() && dq.peekFirst()[1] < left) {
-                    dq.pollFirst();
+                if (!dq.isEmpty() && dq.firstElement()[1] < left) {
+                    dq.remove(0);
                 }
                 // The maximum value of this window is the leftmost value in the 
                 // deque.
-                res[left] = dq.peekFirst()[0];
+                res[left] = dq.firstElement()[0];
                 // Slide the window by advancing both 'left' and 'right'. The right  
                 // pointer always gets advanced so we just need to advance 'left'.
                 left++;

java/Stacks/RepeatedRemovalOfAdjacentDuplicates.java

@@ -1,9 +1,8 @@
-import java.util.ArrayDeque;
-import java.util.Deque;
+import java.util.Stack;
 
 public class RepeatedRemovalOfAdjacentDuplicates {
     public String repeatedRemovalOfAdjacentDuplicates(String s) {
-        Deque<Character> stack = new ArrayDeque<>();
+        Stack<Character> stack = new Stack<>();
         StringBuilder res = new StringBuilder();
         for (char c : s.toCharArray()) {
             // If the current character is the same as the top character on the stack,
@@ -19,7 +18,7 @@ public String repeatedRemovalOfAdjacentDuplicates(String s) {
         }
         // Return the remaining characters as a string.
         for (char c : stack) {
-            res.insert(0, c);
+            res.append(c);
         }
         return res.toString();
     }