Classical Binary Search.java

E 
1521694570
tags: Binary Search

#### Binary Search Template
- while: start + 1 < end
- mid = start + (end - start) / 2;
- 根据mid作比较
- 末尾double check start, end.


```
/*
Find any position of a target number in a sorted array. 
Return -1 if target does not exist.

Example
Given [1, 2, 2, 4, 5, 5].

For target = 2, return 1 or 2.

For target = 5, return 4 or 5.

For target = 6, return -1.

Challenge
O(logn) time

Tags Expand 
Binary Search
*/

/*
Thoughts: classic
start,mid,end
*/
public class Solution {
    public int findPosition(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) >> 1);
            if (nums[mid] == target) {
                return mid;
            } else if (nums[mid] < target) {
                start = mid;
            } else {
                end = mid;
            }
        }

        if (nums[start] == target) {
            return start;
        }
        if (nums[end] == target) {
            return end;
        }
        return -1;
    }
}

```