Binary Search汇总

 1 /*
 2      * For question 2 elements are not distinct
 3      *search both left and right but can shrink searh area
 4      */
 5     public static int magicFast(int[] arr, int start, int end){
 6         if(end < start || start <  0 || end >= arr.length){
 7             return -1;
 8         }
 9         int midIndex = (start + end)/2;
10         int midValue = arr[midIndex];
11         
12         if(midIndex == midValue) return midIndex;
13         
14         //search left
15         int leftIndex = Math.min(midValue, midIndex - 1);
16         int left = magicFast(arr, start, leftIndex);
17         if(left >= 0) return left;
18         
19         //search right
20         int rightIndex = Math.max(midValue, midIndex + 1);
21         int right = magicFast(arr, rightIndex, end);
22         //no need to check
23         
24         return right;
25     }