leetcode-33. Search in Rotated Sorted Array

https://leetcode.com/problems/search-in-rotated-sorted-array/#/description

问题描述：

假设有一个升序的数组围绕着一个固定的轴旋转，给定一个值，若改值在数组中，返回索引值，不在则返回-1；

Suppose an array sorted in ascending order 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.

解题思路:

采用二分查找

因为是升序排列，由于可以旋转，可能有一种情况是4 5 6 0 1 2 3这样，mid指向0则nums[low]>nums[mid]，但是mid右侧是完全按照升序排列，如果是正常顺序，则按照正常的区间。需要考虑是否会出现上面说的那种情况，如果出现，则分区间考虑。target总会在一个全升序的区间当中，如果不在则考虑另一个区间，变换指针。

代码如下：

public class Solution {
public int search(int[] nums, int target) {

if(nums.length==0)return -1;

int low=0;
int high=nums.length-1;

while(low<high)
{
int mid=(low+high)/2;

if(nums[mid]==target)
{
return mid;
}

if(nums[mid]<nums[low])
{
if(target>nums[mid] && target<=nums[high] )
{
low=mid+1;
}else
{
high=mid-1;
}

}else
{

if(target>=nums[low] && target <nums[mid])
{
high=mid-1;
}else
{
low=mid+1;
}

}

}

return nums[low]==target?low:-1;

}
}