# LeetCode 374. Guess Number Higher or Lower

## Description

https://leetcode.com/problems/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 will tell you whether the number I picked is higher or lower than your guess.

You call a pre-defined API `int guess(int num)`, which returns 3 possible results:

• `-1`: The number I picked is lower than your guess (i.e. `pick < num`).
• `1`: The number I picked is higher than your guess (i.e. `pick > num`).
• `0`: The number I picked is equal to your guess (i.e. `pick == num`).

Return the number that I picked.

Example 1:

```Input: n = 10, pick = 6
Output: 6
```

Example 2:

```Input: n = 1, pick = 1
Output: 1
```

Example 3:

```Input: n = 2, pick = 1
Output: 1
```

Example 4:

```Input: n = 2, pick = 2
Output: 2
```

Constraints:

• `1 <= n <= 231 - 1`
• `1 <= pick <= n`

## Explanation

Do a binary search to find the pick.

## Python Solution

``````# The guess API is already defined for you.
# @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
# def guess(num: int) -> int:

class Solution:
def guessNumber(self, n: int) -> int:

start = 1
end = n

while start + 1 < end:
mid = start + (end - start) // 2
if guess(mid) == 0:
return mid
elif guess(mid) == -1:
end = mid
else:
start = mid

if guess(end) == 0:
return end

if guess(start) == 0:
return start

``````
• Time Complexity: O(log(N)).
• Space Complexity: O(1).