374.-guess-number-higher-or-lower.md

374. Guess Number Higher or Lower

• Easy

• 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.

• (This is just binary search

Solution (Python)

# The guess API is already defined for you.
# @param num, your guess
# @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
# def guess(num: int) -> int:

class Solution:
    def guessNumber(self, n: int) -> int:
        l=0
        r=n
        while l<r:
            m=(l+r)//2
            if guess(m)<0:
                r=m-1
            elif guess(m)>0:
                l=m+1
            else:
                return m
        return l

Solution (C)

/** 
 * 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);
 */

int guessNumber(int n){
	long l=0;
    long r=n;
    while (l<r)
    {
        long m=(l+r)/2;
        int answer=guess(m);
        if (answer<0)
        {
            r=m-1;
        }
        else if (answer>0)
        {
            l=m+1;
        }
        else
        {
            return m;
        }
    }
    return l;
}