374. Guess Number Higher or Lower

Problem Description

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 (num > pick)
• 1: Your guess is lower than the number I picked (num < pick)
• 0: your guess is equal to the number I picked (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

Python Solution

# 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:
        left, right = 1, n
        
        while left <= right:
            mid = left + (right - left) // 2
            result = guess(mid)
            
            if result == 0:
                return mid
            elif result == 1:
                left = mid + 1
            else:
                right = mid - 1
        
        return left  # This line should never be reached

Java Solution

/** 
 * 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 extends GuessGame {
    public int guessNumber(int n) {
        int left = 1;
        int right = n;
        
        while (left <= right) {
            int mid = left + (right - left) / 2;
            int result = guess(mid);
            
            if (result == 0) {
                return mid;
            } else if (result == 1) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        
        return left;  // This line should never be reached
    }
}

C++ Solution

/** 
 * 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);
 */

class Solution {
public:
    int guessNumber(int n) {
        int left = 1;
        int right = n;
        
        while (left <= right) {
            int mid = left + (right - left) / 2;
            int result = guess(mid);
            
            if (result == 0) {
                return mid;
            } else if (result == 1) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        
        return left;  // This line should never be reached
    }
};

JavaScript Solution

/** 
 * Forward declaration of guess API.
 * @param {number} 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
 * var guess = function(num) {}
 */

/**
 * @param {number} n
 * @return {number}
 */
var guessNumber = function(n) {
    let left = 1;
    let right = n;
    
    while (left <= right) {
        const mid = left + Math.floor((right - left) / 2);
        const result = guess(mid);
        
        if (result === 0) {
            return mid;
        } else if (result === 1) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
    
    return left;  // This line should never be reached
};

C# Solution

/** 
 * 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;
        int right = n;
        
        while (left <= right) {
            int mid = left + (right - left) / 2;
            int result = guess(mid);
            
            if (result == 0) {
                return mid;
            } else if (result == 1) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        
        return left;  // This line should never be reached
    }
}