binary search完整笔记

 1 public class Solution {
 2     public int search(int[] nums, int target) {
 3         int i = 0, j = nums.length - 1;
 4         while (i + 1 < j) {
 5             int mid = i + (j - i) / 2;
 6             if (nums[mid] == target) {
 7                 return mid;
 8             }
 9             
10             if (nums[mid] < target) {
11                 if (target >= nums[i] && nums[mid] <= nums[i]) {
12                     j = mid;
13                 } else {
14                     i = mid;
15                 }
16             } else {
17                 if (target <= nums[j] && nums[mid] >= nums[j]) {
18                     i = mid;
19                 } else {
20                     j = mid;
21                 }
22             }
23             
24         }
25         if (nums[i] == target) {
26             return i;
27         }
28         if (nums[j] == target) {
29             return j;
30         }
31         return -1;
32     }
33 }

 1 public class Solution {
 2     public int search(int[] A, int target) {
 3         if (A == null || A.length == 0) {
 4             return -1;
 5         }
 6 
 7         int start = 0;
 8         int end = A.length - 1;
 9         int mid;
10         
11         while (start + 1 < end) {
12             mid = start + (end - start) / 2;
13             if (A[mid] == target) {
14                 return mid;
15             }
16             if (A[start] < A[mid]) {
17                 // situation 1, red line
18                 if (A[start] <= target && target <= A[mid]) {
19                     end = mid;
20                 } else {
21                     start = mid;
22                 }
23             } else {
24                 // situation 2, green line
25                 if (A[mid] <= target && target <= A[end]) {
26                     start = mid;
27                 } else {
28                     end = mid;
29                 }
30             }
31         } // while
32         
33         if (A[start] == target) {
34             return start;
35         }
36         if (A[end] == target) {
37             return end;
38         }
39         return -1;
40     }
41 }