Min Stack

Author: nikoo28

src/main/java/leetcode/medium/MinStack.java

@@ -0,0 +1,42 @@
+package leetcode.medium;
+
+import java.util.Stack;
+
+public class MinStack {
+
+  Stack<Integer> stack;
+  Stack<Integer> minStack;
+
+  public MinStack() {
+    stack = new Stack<>();
+    minStack = new Stack<>();
+  }
+
+  public void push(int val) {
+    stack.push(val);
+
+    // If the minStack is empty or the new value is less than or equal to
+    // the top of the minStack, push it onto the minStack
+    if (minStack.isEmpty() || val <= minStack.peek()) {
+      minStack.push(val);
+    }
+  }
+
+  public void pop() {
+    int poppedValue = stack.pop();
+
+    // If the popped value is equal to the top of the minStack,
+    // pop it from the minStack as well
+    if (poppedValue == minStack.peek()) {
+      minStack.pop();
+    }
+  }
+
+  public int top() {
+    return stack.peek();
+  }
+
+  public int getMin() {
+    return minStack.peek();
+  }
+}

src/test/java/leetcode/medium/MinStackTest.java

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+package leetcode.medium;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class MinStackTest {
+
+  @Test
+  void testMinStack1() {
+    MinStack minStack = new MinStack();
+    minStack.push(-2);
+    minStack.push(0);
+    minStack.push(-3);
+    assertEquals(-3, minStack.getMin());
+    minStack.pop();
+    assertEquals(0, minStack.top());
+    assertEquals(-2, minStack.getMin());
+  }
+
+  @Test
+  void testMinStack2() {
+    MinStack minStack = new MinStack();
+    minStack.push(-1);
+    minStack.push(-2);
+    minStack.push(-3);
+    minStack.push(0);
+    minStack.push(2);
+    assertEquals(-3, minStack.getMin());
+    assertEquals(2, minStack.top());
+    minStack.pop();
+    assertEquals(0, minStack.top());
+    assertEquals(-3, minStack.getMin());
+  }
+
+}