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Question

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

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.

 

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

 

Constraints:

  • 1 <= n <= 231 - 1
  • 1 <= pick <= n

Algorithm

Binary search.

Code

  • 
    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;
        }
    }
    
    ############
    
    /**
     * 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 n) {
            int left = 1, right = n;
            while (left < right) {
                int mid = (left + right) >>> 1;
                if (guess(mid) <= 0) {
                    right = mid;
                } else {
                    left = mid + 1;
                }
            }
            return left;
        }
    }
    
  • // 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 num is higher than the picked number
    #          1 if num is lower than the picked number
    #          otherwise return 0
    # def guess(num: int) -> int:
    
    
    class Solution:
        def guessNumber(self, n: int) -> int:
            return bisect.bisect(range(1, n + 1), 0, key=lambda x: -guess(x))
    
    ############
    
    # 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
    
    
  • /**
     * 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
     * func guess(num int) int;
     */
    
    func guessNumber(n int) int {
    	return sort.Search(n, func(i int) bool {
    		i++
    		return guess(i) <= 0
    	}) + 1
    }
    
  • /**
     * Forward declaration of guess API.
     * @param {number} 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
     * var guess = function(num) {}
     */
    
    function guessNumber(n: number): number {
        let l = 1;
        let r = n;
        while (l < r) {
            const mid = (l + r) >>> 1;
            if (guess(mid) <= 0) {
                r = mid;
            } else {
                l = mid + 1;
            }
        }
        return l;
    }
    
    
  • /** 
     * 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 : GuessGame {
        public int GuessNumber(int n) {
            int left = 1, right = n;
            while (left < right) {
                int mid = left + ((right - left) >> 1);
                if (guess(mid) <= 0) {
                    right = mid;
                } else {
                    left = mid + 1;
                }
            }
            return left;
        }
    }
    
  • /**
     * 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
     * unsafe fn guess(num: i32) -> i32 {}
     */
    
    impl Solution {
        unsafe fn guessNumber(n: i32) -> i32 {
            let mut l = 1;
            let mut r = n;
            loop {
                let mid = l + (r - l) / 2;
                match guess(mid) {
                    -1 => r = mid - 1,
                    1 => l = mid + 1,
                    _ => break mid,
                }
            }
        }
    }
    
    

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