[leetcode33Search in Rotated Sorted Array]在排序旋转后序列中找目标值

直接上代码

/**
 * Created by lvhao on 2017/6/30.
 * 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.
 思路是目标值肯定在一个升序子序列中（可能子序列很短，但是肯定存在），目标就是找到这个子序列然后用二分法找到值
 找目标序列的时候也是用二分法，判断的依据是mid值比fin值大的话说明左边是升序，小的话，右边是升序，然后在利用升序序列的的
 首尾值判断目标值是否在里边，在里边就用二分法找值，不在里边就改变fin或者sta值，继续循环找，注意二分法的时候while的判断
 条件是sta<= fin,如果没有=的话，两个数的情况判断不出来。
 */
public class Q33SearchRotatedArray {
    public static void main(String[] args) {
        int[] nums = new int[]{3,1};
        int target = 1;
        int res = search(nums,target);
        System.out.println(res);
 
    }
    public static  int search(int[] nums, int target) {
        int len = nums.length;
        //判断特殊情况
        if(len == 1 && nums[0] == target)
        {
            return 0;
        }
        int sta = 0,fin = len-1,mid,index = -1;
        //注意等号
        while(sta <= fin)
        {
            mid = (sta + fin)/2;
            if(nums[mid] < nums[fin])
            {
                if(target <= nums[fin] && target >= nums[mid])
                {
                    index = binarySearch(nums,mid,fin,target);
                    //找到值之后立即break
                    break;
                }
 
                else
                    fin = mid -1;
            }
            else
            {
                if(target <= nums[mid] && target >= nums[sta])
                {
                    index = binarySearch(nums,sta,mid,target);
                    break;
                }
 
                else
                    sta = mid + 1;
            }
        }
        return index;
    }
    public static int binarySearch(int[] nums,int sta,int fin,int target)
    {
        int mid,index = -1;
        //注意等号
        while (sta <= fin)
        {
            mid = (sta + fin)/2;
            if(target == nums[mid])
            {
                index = mid;
                break;
            }
            else if (target < nums[mid])
                fin = mid-1;
            else
                sta = mid+1;
        }
        return index;
    }
}