Add MinStackUsingSingleStack algorithm (#5759)

src/main/java/com/thealgorithms/stacks/MinStackUsingSingleStack.java

@@ -0,0 +1,65 @@
+package com.thealgorithms.stacks;
+
+import java.util.EmptyStackException;
+import java.util.Stack;
+
+/**
+ * Min-Stack implementation using a single stack.
+ *
+ * This stack supports push, pop, and retrieving the minimum element
+ * in constant time (O(1)) using a modified approach where the stack
+ * stores both the element and the minimum value so far.
+ *
+ * @author Hardvan
+ */
+public class MinStackUsingSingleStack {
+    private final Stack<long[]> stack = new Stack<>();
+
+    /**
+     * Pushes a new value onto the stack.
+     * Each entry stores both the value and the minimum value so far.
+     *
+     * @param value The value to be pushed onto the stack.
+     */
+    public void push(int value) {
+        if (stack.isEmpty()) {
+            stack.push(new long[] {value, value});
+        } else {
+            long minSoFar = Math.min(value, stack.peek()[1]);
+            stack.push(new long[] {value, minSoFar});
+        }
+    }
+
+    /**
+     * Removes the top element from the stack.
+     */
+    public void pop() {
+        if (!stack.isEmpty()) {
+            stack.pop();
+        }
+    }
+
+    /**
+     * Retrieves the top element from the stack.
+     *
+     * @return The top element of the stack.
+     */
+    public int top() {
+        if (!stack.isEmpty()) {
+            return (int) stack.peek()[0];
+        }
+        throw new EmptyStackException();
+    }
+
+    /**
+     * Retrieves the minimum element in the stack.
+     *
+     * @return The minimum element so far.
+     */
+    public int getMin() {
+        if (!stack.isEmpty()) {
+            return (int) stack.peek()[1];
+        }
+        throw new EmptyStackException();
+    }
+}