每天一道LeetCode--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!

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：

374. Guess Number Higher or Lower