LeetCode [374] 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

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// 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) { long long l = 1, r = n; while(l<=r){ long long m = (l+r)/2; int g = guess(m); if(g==0) return m; if(g<0) r = m-1; if(g>0) l = m+1; } return -1; } };