0374 - Guess Number Higher or Lower (Easy)

Problem Link

https://leetcode.com/problems/guess-number-higher-or-lower/

Problem Statement

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 <= 2^31 - 1
• 1 <= pick <= n

Approach 1: Binary Search

See Binary Search for basic understanding.

C++

Written by @wingkwong

/** 
 * 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 l = 1, r = n;
        while (l < r) {
            // middle point
            int m = l + (r - l) / 2;
            // check the result
            int x = guess(m);
            // found the answer
            if (x == 0) return m;
            // exclude m
            else if (x == 1) l = m + 1;
            // include m
            else r = m;
        }
        return l;
    }
};

Rust

Written by @wingkwong

impl Solution {
    unsafe fn guessNumber(n: i32) -> i32 {
        let mut l = 1;
        let mut r = n;
        while l < r {
            let m = l + (r - l) / 2;
            let x = guess(m);
            if x == 1 {
                l = m + 1;
            } else {
                r = m;
            }
        }
        l
    }
}

impl Solution {
    unsafe fn guessNumber(n: i32) -> i32 {
        let mut l = 1;
        let mut r = n;
        loop {
            let m = l + (r - l) / 2;
            match guess(m) {
                -1 => r = m - 1,
                1 => l = m + 1,
                _ => return m
                
            };
        }
    }
}

Python

Written by @radojicic23

# 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 = 1
        right = n
        while left <= right:
            mid = (left + right) // 2
            if guess(mid) == 1:
                left = mid + 1
            elif guess(mid) == -1:
                right = mid
            else:
                return mid

JavaScript

Written by @radojicic23

/** 
 * 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) {
        let mid = Math.floor((left + right) / 2);
        if (guess(mid) === 1) {
            left = mid + 1;
        } else if (guess(mid) === -1) {
            right = mid;
        } else {
            return mid;
        }
    } 
};