LeetCode #374 Guess Number Higher or Lower

Easy

Problem

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

Solution

It’s a classic problem which can be solved by adopting binary search.

Complexity

Obviously, it’s time complexity is O(logn) with only O(1) extra space.