save project

binary_search.py

 # 使用二分查找法，找出9和20在列表里面的索引
-num_list = [1, 3, 5, 8, 11, 15, 17, 18, 20, 21]
\ No newline at end of file
+num_list = [1, 3, 5, 8, 11, 15, 17, 18, 20, 21]
+
+def binary_search(alist,num):
+    low = 0
+    high = len(alist)-1
+    while low <= high:
+        mid = (low + high) // 2
+        guess = alist[mid]
+        if guess == num:
+            return mid
+        elif guess < num:
+            low = mid + 1
+        else:
+            high = mid - 1
+    return None
\ No newline at end of file