374. Guess Number Higher or Lower

Posted 2020-08-13 Machelsky

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.

二分法：最后锁定一个数也就是low=high找到这个数。

/* The guess API is defined in the parent class GuessGame.
   @param num, your guess
   @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
      int guess(int num); */

public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int low=0;
        int high=n;
        
        while(low<high)
        {
            int mid=low+(high-low)/2;
            if(guess(mid)==0)
            {
                return mid;
            }
            else if(guess(mid)==1)
            {
                low=mid+1;
            }
            else
            {
                high=mid-1;
            }
        }
        return low;
        
    }
}