From 57cc0e60890a726f059b164722954ea73df2cd56 Mon Sep 17 00:00:00 2001
From: Peter Chen <sanpeter992000@gmail.com>
Date: Sat, 13 Sep 2025 11:01:40 +0800
Subject: [PATCH] Add solution for the "Merge Sorted Array" problem with unit
 tests.

---
 src/MergeSortedArray88.java                   | 22 -----
 .../com/leetcode/easy/MergeSortedArray88.java | 45 +++++++++++
 .../leetcode/easy/MergeSortedArray88Test.java | 80 +++++++++++++++++++
 3 files changed, 125 insertions(+), 22 deletions(-)
 delete mode 100644 src/MergeSortedArray88.java
 create mode 100644 src/main/java/com/leetcode/easy/MergeSortedArray88.java
 create mode 100644 src/test/java/com/leetcode/easy/MergeSortedArray88Test.java

diff --git a/src/MergeSortedArray88.java b/src/MergeSortedArray88.java
deleted file mode 100644
index c480e2d..0000000
--- a/src/MergeSortedArray88.java
+++ /dev/null
@@ -1,22 +0,0 @@
-public class MergeSortedArray88 {
-    public void merge(int[] nums1, int m, int[] nums2, int n) {
-        int last = m + n - 1;
-        m--;
-        n--;
-        while (m >= 0 && n >= 0) {
-            if (nums1[m] > nums2[n]) {
-                nums1[last] = nums1[m];
-                m--;
-            } else {
-                nums1[last] = nums2[n];
-                n--;
-            }
-            last--;
-        }
-        while (n >= 0) {
-            nums1[last] = nums2[n];
-            n--;
-            last--;
-        }
-    }
-}
diff --git a/src/main/java/com/leetcode/easy/MergeSortedArray88.java b/src/main/java/com/leetcode/easy/MergeSortedArray88.java
new file mode 100644
index 0000000..41557ce
--- /dev/null
+++ b/src/main/java/com/leetcode/easy/MergeSortedArray88.java
@@ -0,0 +1,45 @@
+// Tags: Array, Two Pointers
+package com.leetcode.easy;
+
+public class MergeSortedArray88 {
+    /*
+        Time complexity: O(m + n)
+        Breakdown:
+        -   First while loop: Compares elements from both arrays and places them in the correct position
+            -   In each iteration, either p1 or p2 decrements by 1
+            -   The loop continues until one of the pointers reaches -1
+            -   Maximum iterations: min(m, n)
+        -   Second while loop: Copies remaining elements from nums2 (if any)
+            -   Runs at most n iterations (when all elements from nums2 need to be copied)
+        -   Total operations: Each element from both arrays is processed exactly once
+        -   Overall: O(m + n)
+        Where m is the number of valid elements in nums1 and n is the number of elements in nums2.
+
+        Space complexity: O(1)
+        Breakdown:
+        -   In-place modification: The algorithm modifies nums1 directly without using additional arrays
+        -   Pointer variables: p1, p2, and index use constant space O(1)
+        -   No extra data structures: No additional arrays, lists, or collections are created
+        -   Overall: O(1) - constant space complexity
+     */
+    public void merge(int[] nums1, int m, int[] nums2, int n) {
+        int p1 = m - 1;
+        int p2 = n - 1;
+        int index = m + n - 1;
+        while (p1 >= 0 && p2 >= 0) {
+            if (nums1[p1] >= nums2[p2]) {
+                nums1[index] = nums1[p1];
+                p1--;
+            } else {
+                nums1[index] = nums2[p2];
+                p2--;
+            }
+            index--;
+        }
+        while (p2 >= 0) {
+            nums1[index] = nums2[p2];
+            p2--;
+            index--;
+        }
+    }
+}
diff --git a/src/test/java/com/leetcode/easy/MergeSortedArray88Test.java b/src/test/java/com/leetcode/easy/MergeSortedArray88Test.java
new file mode 100644
index 0000000..8478971
--- /dev/null
+++ b/src/test/java/com/leetcode/easy/MergeSortedArray88Test.java
@@ -0,0 +1,80 @@
+package com.leetcode.easy;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+public class MergeSortedArray88Test {
+    private MergeSortedArray88 solution;
+
+    @BeforeEach
+    void setUp() {
+        solution = new MergeSortedArray88();
+    }
+
+    @Test
+    void testMerge_Example1() {
+        int[] nums1 = {1, 2, 3, 0, 0, 0};
+        int m = 3;
+        int[] nums2 = {2, 5, 6};
+        int n = 3;
+
+        solution.merge(nums1, m, nums2, n);
+
+        int[] expected = {1, 2, 2, 3, 5, 6};
+        assertArrayEquals(expected, nums1);
+    }
+
+    @Test
+    void testMerge_Example2() {
+        int[] nums1 = {1};
+        int m = 1;
+        int[] nums2 = {};
+        int n = 0;
+
+        solution.merge(nums1, m, nums2, n);
+
+        int[] expected = {1};
+        assertArrayEquals(expected, nums1);
+    }
+
+    @Test
+    void testMerge_Example3() {
+        int[] nums1 = {0};
+        int m = 0;
+        int[] nums2 = {1};
+        int n = 1;
+
+        solution.merge(nums1, m, nums2, n);
+
+        int[] expected = {1};
+        assertArrayEquals(expected, nums1);
+    }
+
+    @Test
+    void testMerge_Example4() {
+        int[] nums1 = {4, 5, 6, 0, 0, 0};
+        int m = 3;
+        int[] nums2 = {1, 2, 3};
+        int n = 3;
+
+        solution.merge(nums1, m, nums2, n);
+
+        int[] expected = {1, 2, 3, 4, 5, 6};
+        assertArrayEquals(expected, nums1);
+    }
+
+    @Test
+    void testMerge_Example5() {
+        int[] nums1 = {1, 2, 3, 0, 0, 0};
+        int m = 3;
+        int[] nums2 = {4, 5, 6};
+        int n = 3;
+
+        solution.merge(nums1, m, nums2, n);
+
+        int[] expected = {1, 2, 3, 4, 5, 6};
+        assertArrayEquals(expected, nums1);
+    }
+}