LeetCode 33 Search in Rotated Sorted Array（循环有序数组中进行查找操作）

题目链接：https://leetcode.com/problems/search-in-rotated-sorted-array/?tab=Description

Problem ：当前的数组是一个经过排序之后的循环有序数组，但是该数组的主元选择并不一定是下标为i=0的第一个元素。

例如有序数组为：{1，2，3，4，5，6}

其循环有序数组可能为： {3，4，5，6，1，2}、 {6，1，2，3，4，5}、{4，5，6，1，2，3}等

进行查询操作，使用折半查找。

需要不断判断nums[mid] 与target

以及 target与 nums[start]

和 target与nums[end]的大小关系

if (nums[start] <= nums[mid]){//mid大于startif (target < nums[mid] && target >= nums[start])// target在start和mid之间end = mid - 1;elsestart = mid + 1;
}
if (nums[mid] <= nums[end]){//mid小于endif (target > nums[mid] && target <= nums[end])//target在mid和end之间start = mid + 1;elseend = mid - 1;
}

根据上述的关系，进行对start和end指针的更新操作。

直到 nums[mid] == target时，找到当前下标为mid

循环条件为while(start<=end)

参考代码：

package leetcode_50;/**** * @author pengfei_zheng* 在数组中查找target 并返回其下标*/
public class Solution33 {public int search(int[] nums, int target) {int start = 0;int end = nums.length - 1;while (start <= end){int mid = (start + end) / 2;if (nums[mid] == target)return mid;if (nums[start] <= nums[mid]){if (target < nums[mid] && target >= nums[start]) end = mid - 1;elsestart = mid + 1;} if (nums[mid] <= nums[end]){if (target > nums[mid] && target <= nums[end])start = mid + 1;elseend = mid - 1;}}return -1;}
}

转载于:https://www.cnblogs.com/zpfbuaa/p/6531773.html

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