【每日一算】旋转有序数组

在旋转有序数组中找出给定的一个整数,并返回该整数在数组中的下标?

//常规有序数组
int[] arr1 = {1,2,3,4,5}
//旋转有序数组
int[] arr2 = {50,60,70,80,20,30,40} 

解题思路:

  1. 假设最左边下标用left标识,最右边下标有right标识,中间整数下标用mid标识;
  2. 每次判断下标mid对应的整数值是否大于下标left对应整数值,如果大于,说明左边有序,如果小于,说明右边有序;
  3. 在上一步的基础上,如果左边有序,判断目标值target实在左边还是在右边,如果在左边,right = mid-1,否则 left = mid+1;
  4. 如果右边有序,判断目标值target在左边还是右边,如果在右边,left = mid+1,否则 right = mid -1

代码如下:

public class Solution_2 {

    private static int findTargetIndex(int[] nums, int target) {
        int left = 0;
        int right = nums.length - 1;
        int mid;
        while (left <= right) {
            mid = (right - left) / 2 + left;
            if (nums[mid] == target) {
                return mid;
            }

            if (nums[mid] > nums[left]) {
                //说明在左侧有序
                if (target >= nums[left] && target < nums[mid]) {
                    right = mid - 1;
                } else {
                    left = mid + 1;
                }
            } else {
                //说明在右侧有序
                if (target > nums[mid] && target <= nums[right]) {
                    left = mid + 1;
                } else {
                    right = mid - 1;
                }
            }
        }
        return -1;
    }


    public static void main(String[] args) {
        int[] arr = {10, 20, 30, 40, 1, 2, 3, 4, 5, 6,7};
        int target = 2;
        int targetIndex = findTargetIndex(arr, target);
        System.out.println("targetIndex = " + targetIndex);
    }
}
posted @ 2019-08-23 12:47 qi个名很难么 阅读(...) 评论(...) 编辑 收藏