Binary Search 二分法方法总结

 1 public int BinarySearchTemplate(int[] nums,int target) {
 2         if(nums == null || nums.length == 0) return -1;
 3         int lo = 0;
 4         int hi = nums.length - 1;
 5         
 6         //A: lo < hi [1,2]找1 找last position会死循环
 7         //B: lo <= hi
 8         //C: lo + 1 < hi
 9         //lo  + 1 < hi 相邻就要退出循环，lo = 1，hi = 2
10         while(lo + 1 < hi) {
11             int mid = lo + (hi - lo) / 2;
12             if(nums[mid] == target) 
13                 return mid;
14             else if(nums[mid] < target) {
15                 lo = mid;
16                 //hi = mid - 1 also works，但是不+1/-1更好记
17             }
18             else {
19                 hi = mid;
20                 //lo = mid + 1 also works
21             }
22         }
23         //lo + 1 < hi 方法需要在结尾判断lo和hi
24         if(nums[hi] == target) return hi;
25         if(nums[lo] == target) return lo;
26         
27         return -1;
28     }