Return the largest digit in a number

Beginner Problems Basic Maths Easy

This concept is used widely in validation of inputs or entities in software applications
In banking software or financial applications, you may sometimes have to validate credit card numbers, account numbers, or other numeric inputs where identifying and manipulating the largest digit could be part of the process
Similarly, in gaming and sports applications, stats and scores often involve working with largest digits for comparison and ranking purposes

You are given an integer n. Return the largest digit present in the number.

Examples:

Input: n = 25

Output: 5

Explanation: The largest digit in 25 is 5.

Input: n = 99

Output: 9

Explanation: The largest digit in 99 is 9.

Input: n = 1

Constraints

0 <= n <= 5000
n will contain no leading zeroes except when it is 0 itself.

Company Tags

TCS Cognizant Accenture Infosys Capgemini Wipro IBM HCL Tech Mahindra MindTree

Editorial

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Intuition:

Given a number, all the digits can be extracted from the back (right) successively and the maximum of all the digits can be found by comparing every digit.

Approach:

Initialize a variable largest digit with zero that will store the largest digit in the given number.
The last digit of the original number can be found by using the modulus operator (used to find the remainder for any division) with the number 10.
Iterate on the original number till there are digits left. In every iteration, extract the last (rightmost) digit and check if it is greater than the largest digit. If found greater, update the largest digit with the current digit.
Once the iterations are over, the largest digit in the given number is returned as answer.

Dry Run:

Solution:

#include <bits/stdc++.h>
using namespace std;

class Solution {
public:

    /* Function to find the largest
    digit in a given number*/
    int largestDigit(int n) {
        // Variable to store the largest digit
        int largestDigit = 0;

        /* Keep on iterating while there
        are digits left to extract */
        while(n > 0) {
            int lastDigit = n % 10;

            /* If the current digit is greater than 
            largest digit, update largest digit */
            if(lastDigit > largestDigit) {
                largestDigit = lastDigit;
            }
            
            n = n / 10;
        }
        
        // Return the largest digit 
        return largestDigit;
    }
};

int main()
{
    int n = 348;
    
    /* Creating an instance of 
    Solution class */
    Solution sol; 
    
    // Function call to find the largest digit in n
    int ans = sol.largestDigit(n);
    
    cout << "The largest digit in the number is: " << ans;
    
    return 0;
}
class Solution {

    /* Function to find the largest
    digit in a given number */
    public int largestDigit(int n) {
        // Variable to store the largest digit
        int largestDigit = 0;

        /* Keep on iterating while there
        are digits left to extract */
        while (n > 0) {
            int lastDigit = n % 10;

            /* If the current digit is greater than 
            largest digit, update largest digit */
            if (lastDigit > largestDigit) {
                largestDigit = lastDigit;
            }

            n = n / 10;
        }

        // Return the largest digit
        return largestDigit;
    }

    public static void main(String[] args) {
        int n = 348;

        /* Creating an instance of 
        Solution class */
        Solution sol = new Solution();

        // Function call to find the largest digit in n
        int ans = sol.largestDigit(n);

        System.out.println("The largest digit in the number is: " + ans);
    }
}
class Solution:
    # Function to find the largest
    # digit in a given number
    def largestDigit(self, n):
        # Variable to store the largest digit
        largestDigit = 0

        # Keep on iterating while there
        # are digits left to extract
        while n > 0:
            lastDigit = n % 10

            # If the current digit is greater than 
            # largest digit, update largest digit
            if lastDigit > largestDigit:
                largestDigit = lastDigit

            n = n // 10

        # Return the largest digit
        return largestDigit

if __name__ == "__main__":
    n = 348

    # Creating an instance of 
    # Solution class
    sol = Solution()

    # Function call to find the largest digit in n
    ans = sol.largestDigit(n)

    print("The largest digit in the number is:", ans)
class Solution {
    /* Function to find the largest
    digit in a given number */
    largestDigit(n) {
        // Variable to store the largest digit
        let largestDigit = 0;

        /* Keep on iterating while there
        are digits left to extract */
        while (n > 0) {
            let lastDigit = n % 10;

            /* If the current digit is greater than 
            largest digit, update largest digit */
            if (lastDigit > largestDigit) {
                largestDigit = lastDigit;
            }

            n = Math.floor(n / 10);
        }

        // Return the largest digit
        return largestDigit;
    }
}

const n = 348;

/* Creating an instance of 
Solution class */
const sol = new Solution();

// Function call to find the largest digit in n
const ans = sol.largestDigit(n);

console.log("The largest digit in the number is:", ans);

Complexity Analysis:

Time Complexity: O(log₁₀(N)) – In every iteration, N is divided by 10 (equivalent to the number of digits in N.)

Space Complexity: O(1) – Using a couple of variables i.e., constant space.

Code

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