1 Description #
source: 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 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 <= 2^31 - 11 <= pick <= n
2 Solution #
/**
* Forward declaration of guess API.
* @param num your guess
* @return -1 if num is higher than the picked number
* 1 if num is lower than the picked number
* otherwise return 0
* int guess(int num);
*/
class Solution {
public:
int guessNumber(int n) {
// Time complexity: O(logN)
// Space complexity: O(1)
int low = 1;
int high = n;
int mid = 0;
while(low <= high){
mid = low + (high - low)/2;
int is_lower = guess(mid);
if(is_lower > 0){
low = mid + 1;
}else if(is_lower < 0){
high = mid - 1;
}else{
return mid;
}
}
return mid;
}
};