374. 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 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 three possible results:
-1
: Your guess is higher than the number I picked (i.e.num > pick
).1
: Your guess is lower than the number I picked (i.e.num < pick
).0
: your guess is equal to the number I picked (i.e.num == pick
).
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
Constraints:
1 <= n <= 231 - 1
1 <= pick <= n
Solutions
Solution 1: Binary Search
We perform a binary search in the interval $[1,..n]$, and find the first number that satisfies guess(x) <= 0
, which is the answer.
The time complexity is $O(\log n)$, where $n$ is the upper limit given in the problem. The space complexity is $O(1)$.
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