leetcode 【 Find Minimum in Rotated Sorted Array 】python 实现

题目：

Suppose a sorted array is rotated at some pivot unknown to you beforehand.

(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

Find the minimum element.

You may assume no duplicate exists in the array.

代码：oj测试通过 Runtime: 52 ms

 1 class Solution:
 2     # @param num, a list of integer
 3     # @return an integer
 4     def findMin(self, num):
 5         # none case
 6         if num is None:
 7             return None
 8         # short lenght case
 9         if len(num)==1 :
10             return num[0]
11         # binary search
12         start = 0
13         end = len(num)-1
14         while start<=end :
15             if start==end :
16                 return num[start]
17             if start+1==end :
18                 return min(num[start],num[end])
19             mid = (start+end)/2
20             if num[mid]>num[start] :
21                 if num[mid]>num[end] :
22                     start = mid
23                 else:
24                     return num[start]
25             else:
26                 if num[mid]>num[end] :
27                     return num[end]
28                 else:
29                     end = mid

思路：

基本思路还是binary search。

注意修改start或end时的条件：因为mid也有可能是最小值，所以start=mid end=mid，这个跟传统二分查找时start=mid+1以及end=mid-1有所不同。

想明白这些后，代码一次AC。