LeetCode 374 Guess Number Higher or Lower

Posted 2020-08-06

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:

n = 10, I pick 6.

Return 6.

 

思路：

二分查找即可，注意中间数值不能溢出，因此(high + low) / 2写成low + (high - low) / 2。

 

解法：

 1 /* The guess API is defined in the parent class GuessGame.
 2    @param num, your guess
 3    @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
 4       int guess(int num); 
 5 */
 6 
 7 public class Solution extends GuessGame
 8 {
 9     public int guessNumber(int n)
10     {
11         int low = 1;
12         int high = n;
13         int middle, guessOutcome;
14 
15         while(low <= high)
16         {
17             middle = low + (high - low) / 2;
18             guessOutcome = guess(middle);
19 
20             if(guessOutcome == 1)
21                 low = middle + 1;
22             else if(guessOutcome == -1)
23                 high = middle - 1;
24             else
25                 return middle;
26         }
27 
28         return 0;
29     }
30 }