Question

Formatted question description: https://leetcode.ca/all/374.html

 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 :

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

Algorithm

Binary search.

Code

Java

public class Guess_Number_Higher_or_Lower {


    public class Solution extends GuessGame {
        public int guessNumber(int n) {
            int low = 1;
            int high = n;
            while (low <= high) {
                int mid = low + (high - low) / 2;
                int res = guess(mid);
                if (res == 0)
                    return mid;
                else if (res < 0)
                    high = mid - 1;
                else
                    low = mid + 1;
            }
            return -1;
        }
    }
}

// stub
class GuessGame {
    public int guess(int i) {
        return 0;
    }
}

// OJ: https://leetcode.com/problems/guess-number-higher-or-lower/
// Time: O(logN)
// Space: O(1)
class Solution {
public:
    int guessNumber(int n) {
        int L = 1, R = n;
        while (L <= R) {
            int M = L + (R - L) / 2, g = guess(M);
            if (g == 0) return M;
            if (g == 1) L = M + 1;
            else R = M - 1;
        }
        return -1;
    }
};

# 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):

class Solution(object):
  def guessNumber(self, n):
    """
    :type n: int
    :rtype: int
    """
    l, r = 1, n
    while l < r:
      m = l + (r - l) / 2
      g = guess(m)
      if g == -1:
        r = m - 1
      elif g == 1:
        l = m + 1
      else:
        return m
    return l

374 - Guess Number Higher or Lower

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