【二分查找】374. 猜数字大小

题目：

 

 

解答：

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

class Solution {
public:
    int guessNumber(int n) 
    {
        int low = 1;
        int high = n;
        while (low <= high) 
        {
            int mid = low + (high - low) / 2;
            int res = guess(mid);
            if (res == 0)
                return mid;
            else if (res < 0)
                high = mid - 1;
            else
                low = mid + 1;
        }
        return -1;
    }
};