[33]Search in Rotated Sorted Array

【题目描述】

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

).

You are given a target value to search. If found in the array return its index, otherwise return -1.

You may assume no duplicate exists in the array.

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【思路】

二分搜索。将数列从循环的地方分成左右两部分，分成三种情况考虑：

1.如果nums[mid]>nums[high],说明mid在左半部分

2.如果nums[mid]<nums[low]，说明mid在右半部分

3.反之则说明数列未移动。

【代码】

class Solution {
public:
int search(vector<int>& nums, int target) {
int n=nums.size();
int low,high,mid;
low=0;
high=n-1;
while(low<=high){
mid=(low+high)/2;
if(nums[mid]==target) return mid;
if(nums[high]<nums[mid]){
if(nums[low]<=target&&nums[mid]>target) high=mid-1;
else low=mid+1;
}
else if(nums[low]>nums[mid]){
if(nums[mid]<target&&nums[high]>=target) low=mid+1;
else high=mid-1;
}
else{
if(nums[mid]<target) low=mid+1;
else high=mid-1;
}
}
return -1;
}
};