问题描述:

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.

二分搜索问题.

// Forward declaration of guess API.
// @param num, your guess
// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num);

class Solution {
public:
    int guessNumber(int n) {
        int mid = n / 2, left = 1, right = n, tmpResult;
        while((tmpResult = guess(mid)) != 0){
            if(tmpResult == -1){
                right = mid;
            }
            else if(tmpResult == 1){
                left = mid + 1;
            }
            mid = (right - left) / 2 + left;
        }
        return mid;
    }
};