374. Guess Number Higher or Lower

题目：

We are playing the Guess Game. The game is as follows:

I pick a number from 1 to n. You have to guess which number I picked.

Every time you guess wrong, I'll tell you whether the number is higher or lower.

You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0):

-1 : My number is lower 1 : My number is higher 0 : Congrats! You got it!

Example:

n = 10, I pick 6.Return 6.

思路：

本题很简单，用二分查找法

代码：

// Forward declaration of guess API.// @param num, your guess// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0int guess(int num);class Solution {public:    int guessNumber(int n) {        //simple binary search : low = 1; high = n        int low = 1;        while(low <= n){            int mid = low + (n-low) / 2;            int res = guess(mid);            if(res == 0)                return mid;            else if(res == -1)                n = mid - 1;            else                low = mid + 1;        }        return -1;    }};