文章目录
一、题目
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
二、题解
cpp
/**
* 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) {
int l = 1,r = n;
while(l <= r){
int mid = l + ((r - l) >> 1);
if(guess(mid) == 0) return mid;
else if(guess(mid) == 1) l = mid + 1;
else r = mid - 1;
}
return 0;
}
};