374. Guess Number Higher or Lower

Posted 2021-01-17 ruruozhenhao

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

 

Approach #1:

// 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 l = 1, r = n;
        while (l <= r) {
            int m = l + (r - l) / 2;
            //cout << m << endl;
            if (guess(m) == 1) l = m + 1;
            else if (guess(m) == -1) r = m - 1;
            else return m;
        }
        return -1;
    }
};

Runtime: 0 ms, faster than 100.00% of C++ online submissions for Guess Number Higher or Lower.

 

Analysis:

you should pay attention to that My number is lower  represent pick > m.