From a18ee1e5d78f182298c062030f1e277f82faa72a Mon Sep 17 00:00:00 2001
From: Sainnhe Park <i@sainnhe.dev>
Date: Mon, 21 Nov 2022 20:04:27 +0800
Subject: [PATCH] Add bin_search.md

---
 notes/src/SUMMARY.md    |  1 +
 notes/src/bin_search.md | 57 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)
 create mode 100644 notes/src/bin_search.md

diff --git a/notes/src/SUMMARY.md b/notes/src/SUMMARY.md
index 095b11b..50d07d6 100644
--- a/notes/src/SUMMARY.md
+++ b/notes/src/SUMMARY.md
@@ -6,3 +6,4 @@
 ## 经典代码
 
 - [合并两个有序链表](./merge_two_sorted_linked_lists.md)
+- [二分查找](./bin_search.md)
diff --git a/notes/src/bin_search.md b/notes/src/bin_search.md
new file mode 100644
index 0000000..f758205
--- /dev/null
+++ b/notes/src/bin_search.md
@@ -0,0 +1,57 @@
+# 二分查找
+
+非递归：
+
+```cpp
+/**
+ * 二分查找普通实现。
+ * @param srcArray 有序数组
+ * @param key 查找元素
+ * @return  不存在返回-1
+ */
+public
+static int binSearch(int srcArray[], int key) {
+  int mid;
+  int start = 0;
+  int end = srcArray.length - 1;
+  while (start <= end) {
+    mid = (end - start) / 2 + start;
+    if (key < srcArray[mid]) {
+      end = mid - 1;
+    } else if (key > srcArray[mid]) {
+      start = mid + 1;
+    } else {
+      return mid;
+    }
+  }
+  return -1;
+}
+```
+
+递归：
+
+```cpp
+/**
+ * 二分查找递归实现。
+ * @param srcArray  有序数组
+ * @param start 数组低地址下标
+ * @param end   数组高地址下标
+ * @param key  查找元素
+ * @return 查找元素不存在返回-1
+ */
+public
+static int binSearch(int srcArray[], int start, int end, int key) {
+  int mid = (end - start) / 2 + start;
+  if (srcArray[mid] == key) {
+    return mid;
+  }
+  if (start >= end) {
+    return -1;
+  } else if (key > srcArray[mid]) {
+    return binSearch(srcArray, mid + 1, end, key);
+  } else if (key < srcArray[mid]) {
+    return binSearch(srcArray, start, mid - 1, key);
+  }
+  return -1;
+}
+```