From c14ca74b8b720cd9a0738f6484282743e4976943 Mon Sep 17 00:00:00 2001
From: hpstory <33348162+hpstory@users.noreply.github.com>
Date: Sun, 6 Aug 2023 23:16:02 +0800
Subject: [PATCH] feat(csharp): add binary search csharp codes (#676)

---
 .../chapter_searching/binary_search_edge.cs   | 50 +++++++++++++++
 .../binary_search_insertion.cs                | 64 +++++++++++++++++++
 .../binary_search_insertion.java              |  2 +-
 3 files changed, 115 insertions(+), 1 deletion(-)
 create mode 100644 codes/csharp/chapter_searching/binary_search_edge.cs
 create mode 100644 codes/csharp/chapter_searching/binary_search_insertion.cs

diff --git a/codes/csharp/chapter_searching/binary_search_edge.cs b/codes/csharp/chapter_searching/binary_search_edge.cs
new file mode 100644
index 000000000..4238ec935
--- /dev/null
+++ b/codes/csharp/chapter_searching/binary_search_edge.cs
@@ -0,0 +1,50 @@
+/**
+* File: binary_search_edge.cs
+* Created Time: 2023-08-06
+* Author: hpstory (hpstory1024@163.com)
+*/
+
+namespace hello_algo.chapter_searching;
+
+public class binary_search_edge {
+    /* 二分查找最左一个 target */
+    public int binarySearchLeftEdge(int[] nums, int target) {
+        // 等价于查找 target 的插入点
+        int i = binary_search_insertion.binarySearchInsertion(nums, target);
+        // 未找到 target ，返回 -1
+        if (i == nums.Length || nums[i] != target) {
+            return -1;
+        }
+        // 找到 target ，返回索引 i
+        return i;
+    }
+
+    /* 二分查找最右一个 target */
+    public int binarySearchRightEdge(int[] nums, int target) {
+        // 转化为查找最左一个 target + 1
+        int i = binary_search_insertion.binarySearchInsertion(nums, target + 1);
+        // j 指向最右一个 target ，i 指向首个大于 target 的元素
+        int j = i - 1;
+        // 未找到 target ，返回 -1
+        if (j == -1 || nums[j] != target) {
+            return -1;
+        }
+        // 找到 target ，返回索引 j
+        return j;
+    }
+
+    [Test]
+    public void Test() {
+        // 包含重复元素的数组
+        int[] nums = { 1, 3, 6, 6, 6, 6, 6, 10, 12, 15 };
+        Console.WriteLine("\n数组 nums = " + nums.PrintList());
+
+        // 二分查找左边界和右边界
+        foreach (int target in new int[] { 6, 7 }) {
+            int index = binarySearchLeftEdge(nums, target);
+            Console.WriteLine("最左一个元素 " + target + " 的索引为 " + index);
+            index = binarySearchRightEdge(nums, target);
+            Console.WriteLine("最右一个元素 " + target + " 的索引为 " + index);
+        }
+    }
+}
diff --git a/codes/csharp/chapter_searching/binary_search_insertion.cs b/codes/csharp/chapter_searching/binary_search_insertion.cs
new file mode 100644
index 000000000..5dac69830
--- /dev/null
+++ b/codes/csharp/chapter_searching/binary_search_insertion.cs
@@ -0,0 +1,64 @@
+/**
+* File: binary_search_insertion.cs
+* Created Time: 2023-08-06
+* Author: hpstory (hpstory1024@163.com)
+*/
+
+namespace hello_algo.chapter_searching;
+
+public class binary_search_insertion {
+    /* 二分查找插入点（无重复元素） */
+    public int binarySearchInsertionSimple(int[] nums, int target) {
+        int i = 0, j = nums.Length - 1; // 初始化双闭区间 [0, n-1]
+        while (i <= j) {
+            int m = i + (j - i) / 2; // 计算中点索引 m
+            if (nums[m] < target) {
+                i = m + 1; // target 在区间 [m+1, j] 中
+            } else if (nums[m] > target) {
+                j = m - 1; // target 在区间 [i, m-1] 中
+            } else {
+                return m; // 找到 target ，返回插入点 m
+            }
+        }
+        // 未找到 target ，返回插入点 i
+        return i;
+    }
+
+    /* 二分查找插入点（存在重复元素） */
+    public static int binarySearchInsertion(int[] nums, int target) {
+        int i = 0, j = nums.Length - 1; // 初始化双闭区间 [0, n-1]
+        while (i <= j) {
+            int m = i + (j - i) / 2; // 计算中点索引 m
+            if (nums[m] < target) {
+                i = m + 1; // target 在区间 [m+1, j] 中
+            } else if (nums[m] > target) {
+                j = m - 1; // target 在区间 [i, m-1] 中
+            } else {
+                j = m - 1; // 首个小于 target 的元素在区间 [i, m-1] 中
+            }
+        }
+        // 返回插入点 i
+        return i;
+    }
+
+    [Test]
+    public void Test() {
+        // 无重复元素的数组
+        int[] nums = { 1, 3, 6, 8, 12, 15, 23, 26, 31, 35 };
+        Console.WriteLine("\n数组 nums = " + nums.PrintList());
+        // 二分查找插入点
+        foreach (int target in new int[] { 6, 9 }) {
+            int index = binarySearchInsertionSimple(nums, target);
+            Console.WriteLine("元素 " + target + " 的插入点的索引为 " + index);
+        }
+
+        // 包含重复元素的数组
+        nums = new int[] { 1, 3, 6, 6, 6, 6, 6, 10, 12, 15 };
+        Console.WriteLine("\n数组 nums = " + nums.PrintList());
+        // 二分查找插入点
+        foreach (int target in new int[] { 2, 6, 20 }) {
+            int index = binarySearchInsertion(nums, target);
+            Console.WriteLine("元素 " + target + " 的插入点的索引为 " + index);
+        }
+    }
+}
diff --git a/codes/java/chapter_searching/binary_search_insertion.java b/codes/java/chapter_searching/binary_search_insertion.java
index cacf553a0..8bfcb802c 100644
--- a/codes/java/chapter_searching/binary_search_insertion.java
+++ b/codes/java/chapter_searching/binary_search_insertion.java
@@ -1,5 +1,5 @@
 /**
- * File: binary_search_edge.java
+ * File: binary_search_insertion.java
  * Created Time: 2023-08-04
  * Author: Krahets (krahets@163.com)
  */