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start
if (target < nums[mid] && target >= nums[start])// target在start和mid之间
end = mid - 1;
else
start = mid + 1;
}
if (nums[mid] <= nums[end]){//mid小于end
if (target > nums[mid] && target <= nums[end])//target在mid和end之间
start = mid + 1;
else
end = 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;
else
start = mid + 1;
}
if (nums[mid] <= nums[end]){
if (target > nums[mid] && target <= nums[end])
start = mid + 1;
else
end = mid - 1;
}
}
return -1;
}
}
 

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