Add solution for "Binary Search" with unit tests.

src/main/java/com/leetcode/easy/BinarySearch704.java

@@ -0,0 +1,31 @@
+// Tags: Array, Binary Search
+package com.leetcode.easy;
+
+public class BinarySearch704 {
+    /*
+        Let n be the size of the input array nums.
+
+        Time complexity: O(log n)
+        nums is divided into half each time.
+        In the worst-case scenario, we need to cut nums until the range has no element,
+        and it takes logarithmic time to reach this break condition.
+
+        Space complexity: O(1)
+        During the loop, we only need to record three indexes, left, right, and mid, they take constant space.
+     */
+    public int search(int[] nums, int target) {
+        int left = 0;
+        int right = nums.length - 1;
+        while (left <= right) {
+            int mid = left + (right - left) / 2;
+            if (nums[mid] == target) {
+                return mid;
+            } else if (target > nums[mid]) {
+                left = mid + 1;
+            } else {
+                right = mid - 1;
+            }
+        }
+        return -1;
+    }
+}

src/test/java/com/leetcode/easy/BinarySearch704Test.java

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+package com.leetcode.easy;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class BinarySearch704Test {
+    private BinarySearch704 solution;
+
+    @BeforeEach
+    void setUp() {
+        solution = new BinarySearch704();
+    }
+
+    @Test
+    void testSearch_Example1() {
+        int[] nums = {-1, 0, 3, 5, 9, 12};
+        int target = 9;
+
+        int result = solution.search(nums, target);
+
+        assertEquals(4, result);
+    }
+
+    @Test
+    void testSearch_Example2() {
+        int[] nums = {-1, 0, 3, 5, 9, 12};
+        int target = 2;
+
+        int result = solution.search(nums, target);
+
+        assertEquals(-1, result);
+    }
+}