Search in Rotated Sorted Array

最新推荐文章于 2022-02-06 18:22:23 发布

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#Search #Rotated Sorted Array

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本文介绍了一种在旋转过的有序数组中查找特定元素的方法。通过两次二分查找确定目标元素的位置，首先找到旋转点，然后根据旋转后的数组进行查找。文章提供了一个Java实现示例。

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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.

代码如下：

public class SearchInRotatedSortedArray {

	public int search(int[] nums,int target){
		int n = nums.length;
		 
        if(nums == null || n <=0)
            return -1;
        
		int lo = 0, hi = n-1;
		
		while(lo<hi){
			int mid = (lo + hi) / 2;
			if(nums[mid] > nums[hi])
				lo = mid + 1;
			else hi = mid;
		}
		int rot = lo;//找到lo==hi时，是最小数的位置，也是旋转的位数
		
		lo = 0;
		hi = n-1;
		
		while(lo<hi){
			int mid = (lo+hi)/2;
			int realmid = (mid+rot)%n;
			if(nums[realmid]==target)
				return realmid;
			if(nums[realmid]<target)
				lo=mid+1;
			else
				hi = mid-1;
		}
		return -1;
	}
	
}