374. 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’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!


n = 10, I pick 6.

Return 6.


1.第一个坑是:其实第一次的时候是把题目的 guess 反回的值理解反了




/* 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 = 1,high = n;
            while (low<high){
                int tmp = low+(high-low)/2;
                int result = guess(tmp);
                if(result == 1)
                    low = tmp+1;
                if (result == -1)
                    high = tmp;
                    return tmp;
            return low;