[容易]二分查找

题目来源：http://www.lintcode.com/zh-cn/problem/first-position-of-target/

可以accept的程序如下（用了STL）：

 1 class Solution {
 2 public:
 3     /**
 4      * @param nums: The integer array.
 5      * @param target: Target number to find.
 6      * @return: The first position of target. Position starts from 0.
 7      */
 8     int binarySearch(vector<int> &array, int target) {
 9         // write your code here
10         vector<int>::iterator p;
11         p=find(array.begin(),array.end(),target);
12         if(p!=array.end())
13             return p-array.begin();
14         else
15             return -1;
16     }
17 };