# 374-guess-number-higher-or-lower

## Question

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

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.
``````

## Thought Process

1. Binary Search
1. Very Typical binary search, where we return when we get 0, search the lower half when we got -1 (the solution is lower), otherwise we search the higher half
2. Time complexity O(nlogn)
3. Space complexity O(1)

## Solution

``````/* The guess API is defined in the parent class GuessGame.
@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 lo = 0, hi = n;
int mid;
while (lo <= hi) {
mid = lo + (hi - lo)/2;
int g = guess(mid);
if (g == 0) return mid;
else if (g > 0) lo = mid + 1;
else hi = mid - 1;
}
return -1;
}
}
``````