guess-number-higher-or-lower.cpp

//question//

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);
 */

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