374. Guess Number Higher or Lower.java

/*
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 3 possible results:

-1: The number I picked is lower than your guess (i.e. pick < num).
1: The number I picked is higher than your guess (i.e. pick > num).
0: The number I picked is equal to your guess (i.e. pick == num).
Return the number that I picked.

 

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
Example 4:

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

Constraints:

1 <= n <= 231 - 1
1 <= pick <= n
*/

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


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