# Question

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.
```

# Solution

```
/* The guess API is defined in the parent class GuessGame.
@param num, your guess
@return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num); */
public class Solution extends GuessGame {
public int guessNumber(int n) {
int l = 1, r = n;
while(r - l > 1) {
int mid = l + (h - l) / 2; // be careful of overflow
int g = guess(mid);
if (g == 0) return mid;
else if(g == 1) l = mid;
else r = mid;
}
return guess(l) == 0 ? l : r;
}
}
```