LeetCode - 374. Guess Number Hiher or Lower(Binary Search, Interactive)

문제

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 will tell you whether the number I picked is higher or lower than your guess.
You call a pre-defined API int guess(int num), which returns three possible results:
-1: Your guess is higher than the number I picked (i.e. num > pick).
1: Your guess is lower than the number I picked (i.e. num < pick).
0: your guess is equal to the number I picked (i.e. num == pick).
Return the number that I picked.

https://leetcode.com/problems/guess-number-higher-or-lower/

Example 1:

Input: n = 10, pick = 6
Output: 6

Example 2:

Input: n = 1, pick = 1
Output: 1

Example 3:

Input: n = 2, pick = 1
Output: 1

풀이

/** 
 * Forward declaration of guess API.
 * @param  num   your guess
 * @return 	     -1 if num is higher than the picked number
 *			      1 if num is lower than the picked number
 *               otherwise return 0
 * int guess(int num);
 */

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