update 155

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/firstthousand/_155.java

@@ -5,9 +5,8 @@
 import java.util.Stack;
 
 public class _155 {
-
     public static class Solution1 {
-        class MinStack {
+        public static class MinStack {
             private Stack<Integer> stack;
             private int min;
 
@@ -17,9 +16,9 @@ public MinStack() {
             }
 
             public void push(int x) {
-                /**All the trick happens here, we push the second minimum number onto the stack before we push the newer one,
-                 * this way, when popping, we could always get the next minimum one in constant time.*/
                 if (x <= min) {
+                    /**All the trick happens here, we push the second minimum number onto the stack before we push the newer one,
+                     * this way, when popping, we could always get the next minimum one in constant time.*/
                     stack.push(min);
                     min = x;
                 }
@@ -49,7 +48,7 @@ public static class Solution2 {
          * We could store a pair onto the stack: the first element in the pair is the value itself,
          * the second element in the pair is the current minimum element so far seen on the stack.
          */
-        class MinStack {
+        public static class MinStack {
             Deque<int[]> stack;
 
             public MinStack() {
@@ -60,7 +59,7 @@ public void push(int val) {
                 if (!stack.isEmpty()) {
                     int[] last = stack.peekLast();
                     int currentMin = last[1];
-                    if (val < currentMin) {
+                    if (val <= currentMin) {
                         stack.addLast(new int[]{val, val});
                     } else {
                         stack.addLast(new int[]{val, currentMin});
@@ -82,6 +81,5 @@ public int getMin() {
                 return stack.peekLast()[1];
             }
         }
-
     }
 }

src/test/java/com/fishercoder/firstthousand/_155Test.java

@@ -0,0 +1,41 @@
+package com.fishercoder.firstthousand;
+
+import com.fishercoder.solutions.firstthousand._155;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class _155Test {
+    private static _155.Solution1.MinStack minStack1;
+    private static _155.Solution2.MinStack minStack2;
+
+    @BeforeEach
+    public void setup() {
+        minStack1 = new _155.Solution1.MinStack();
+        minStack2 = new _155.Solution2.MinStack();
+    }
+
+    @Test
+    public void test1() {
+        minStack1.push(-2);
+        minStack1.push(0);
+        minStack1.push(-3);
+        assertEquals(-3, minStack1.getMin());
+        minStack1.pop();
+        assertEquals(0, minStack1.top());
+        assertEquals(-2, minStack1.getMin());
+    }
+
+    @Test
+    public void test2() {
+        minStack2.push(-2);
+        minStack2.push(0);
+        minStack2.push(-3);
+        assertEquals(-3, minStack2.getMin());
+        minStack2.pop();
+        assertEquals(0, minStack2.top());
+        assertEquals(-2, minStack2.getMin());
+    }
+
+}