#Leetcode# 374. Guess Number Higher or Lower

https://leetcode.com/problems/guess-number-higher-or-lower/

 

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 :

Input: n = 10, pick = 6
Output: 6

题解：二分法 

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 0
int guess(int num);

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