# 【每日一算】旋转有序数组

//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} 

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

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