添加 二分查找算法

Author: amusi

Data Structures and Algorithms/README.md

@@ -2,7 +2,7 @@
 
 [排序算法](sort)
 
-
+[查找算法](search)
 
 
 

Data Structures and Algorithms/search/README.md

@@ -0,0 +1,37 @@
+# 二分查找
+
+二分查找（Binary Search）是将查找的键和子数组的中间键作比较，如果被查找的键小于中间键，就在左子数组继续查找；如果大于中间键，就在右子数组中查找，否则中间键就是要找的元素。
+
+[Python代码](binary_search.py)：
+
+```python
+import math
+
+def BinarySearch(arr, key):
+    left = 0
+    right = len(arr)-1
+
+    while left <= right:
+        mid = math.ceil((left+right)/2)
+        if arr[mid] == key:
+            return 1
+        elif arr[mid]<key:
+            left = mid+1
+        else:
+            right = mid-1
+    return 0
+
+
+arr = [10,20,-9,-10,100,-100,77,88,33,21]
+arr.sort()
+if BinarySearch(arr, -9):
+    print("Yes")
+else:
+    print("No")
+```
+
+参考：
+
+[二分查找(Binary Search)](https://www.cnblogs.com/yedushusheng/p/5524166.html)
+
+[你真的会写二分查找吗](https://www.cnblogs.com/luoxn28/p/5767571.html)

Data Structures and Algorithms/search/binary_search.py

@@ -0,0 +1,23 @@
+import math
+
+def BinarySearch(arr, key):
+    left = 0
+    right = len(arr)-1
+
+    while left <= right:
+        mid = math.ceil((left+right)/2)
+        if arr[mid] == key:
+            return 1
+        elif arr[mid]<key:
+            left = mid+1
+        else:
+            right = mid-1
+    return 0
+
+
+arr = [10,20,-9,-10,100,-100,77,88,33,21]
+arr.sort()
+if BinarySearch(arr, -9):
+    print("Yes")
+else:
+    print("No")