二分查找的时间复杂度是 O(log n)，但难点在于判断左右边界和边界条件。

一、基础二分

publicintbinarySearch(int[]nums,inttarget){intleft=0,right=nums.length-1;while(left<=right){intmid=left+(right-left)/2;if(nums[mid]==target)returnmid;if(nums[mid]<target)left=mid+1;elseright=mid-1;}return-1;}

二、搜索旋转排序数组

publicintsearch(int[]nums,inttarget){intleft=0,right=nums.length-1;while(left<=right){intmid=left+(right-left)/2;if(nums[mid]==target)returnmid;if(nums[left]<=nums[mid]){if(target>=nums[left]&&target<nums[mid])right=mid-1;elseleft=mid+1;}else{if(target>nums[mid]&&target<=nums[right])left=mid+1;elseright=mid-1;}}return-1;}

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