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:

n = 10, I pick 6.

Return 6.

This can be easily solved using binary search

int guess(int num);

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

return -1;
}
};