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.

解法一：  递归

public int guessNumber(int n) {        return guessNumber(1, n);    }    /*递归*/    private  int guessNumber(int start,int end){        int mid=start+(end-start)/2;        if(guess(mid)==-1){            return guessNumber(start,mid-1);        }else        if(guess(mid)==1){            return guessNumber(mid+1,end);        }else{            return mid;        }    }}

解法二：循环

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

其他解法，参考：