Q:For a given sorted array (ascending order) and a target number, find the first index of this number in O(log n) time complexity. If the target number does not exist in the array, return -1.
A: binary search
public int binarySearch(int[] nums, int target){
if (nums == null || nums.length == 0) return -1;
int start = 0;
int end = nums.length - 1;
while (start + 1 < end){
int mid = start + (end - start) / 2;
if (nums[mid] >= target) end = mid;
else start = mid;
}
if (nums[start] == target) return start;
else if (nums[end] == target) return end;
else return -1;
}
Lintcode 14 First Position of Target
原文：http://www.cnblogs.com/nobody2somebody/p/5146293.html