First Position of Target

 1 class Solution {
 2     /**
 3      * @param nums: The integer array.
 4      * @param target: Target to find.
 5      * @return: The first position of target. Position starts from 0.
 6      */
 7     public int binarySearch(int[] nums, int target) {
 8         if (nums == null || nums.length == 0) return -1;
 9         
10         int start = 0;
11         int end = nums.length - 1;
12         
13         while (start <= end) {
14             int mid = start + (end - start) / 2;
15             if (nums[mid] == target) {
16                 if (mid != 0 && nums[mid - 1] == target) {
17                     end = mid - 1;
18                 } else {
19                     return mid;
20                 }
21             } else if (nums[mid] < target) {
22                 start = mid + 1;
23             } else {
24                 end = mid - 1;
25             }
26         }
27         return -1;
28     }
29 }