Number with even sum of digits
A positive integer is considered a good number if sum of its digits is even. Find n-th smallest good number.
Examples :
Input : n = 1 Output : 2 First good number is smallest positive number with sum of digits even which is 2. Input : n = 10 Output : 20
A simple solution is to start from 1 and traverse through all natural numbers. For every number x, check if sum of digits is even. If even increment count of good numbers. Finally return the n-th Good number.
An efficient solution is based on a pattern in the answer. Let us list down first 20 good numbers. The first 20 good numbers are: 2, 4, 6, 8, 11, 13, 15, 17, 19, 20, 22, 24, 26, 28, 31, 33, 35, 37, 39, 40. Observe that if last digit of n is from 0 to 4 the answer is 2*n and if last digit of n is from 5 to 9 the answer is 2*n + 1.
C++
// C++ program to find n-th // Good number. #include <bits/stdc++.h> using namespace std; // Function to find kth good number. long long int findKthGoodNo(long long int n) { // Find the last digit of n. int lastDig = n % 10; // If last digit is between // 0 to 4 then return 2 * n. if (lastDig >= 0 && lastDig <= 4) return n << 1; // If last digit is between // 5 to 9 then return 2*n + 1. else return (n << 1) + 1; } // Driver code int main() { long long int n = 10; cout << findKthGoodNo(n); return 0; } |
chevron_right
filter_none
Java
// Java program to find n-th // Good number. class GFG { // Function to find kth good number. static int findKthGoodNo(int n) { // Find the last digit of n. int lastDig = n % 10; // If last digit is between // 0 to 4 then return 2*n. if (lastDig >= 0 && lastDig <= 4) return n << 1; // If last digit is between // 5 to 9 then return 2*n + 1. else return (n << 1) + 1; } // Driver code public static void main(String[] args) { int n = 10; System.out.println(findKthGoodNo(n)); } } // This code is contributed by // Smitha Dinesh Semwal |
chevron_right
filter_none
Python 3
# Python 3 program to find # n-th Good number. # Function to find kth # good number. def findKthGoodNo(n): # Find the last digit of n. lastDig = n % 10 # If last digit is between # 0 to 4 then return 2 * n. if (lastDig >= 0 and lastDig <= 4) : return n << 1 # If last digit is between # 5 to 9 then return 2 * n + 1. else: return (n << 1) + 1 # Driver code n = 10print(findKthGoodNo(n)) # This code is contributed by # Smitha Dinesh Semwal |
chevron_right
filter_none
C#
// C# program to find n-th // Good number. using System; class GFG { // Function to find kth // good number public static int findKthGoodNo(int n) { // Find the last digit of n. int lastDig = n % 10; // If last digit is between // 0 to 4 then return 2*n. if (lastDig >= 0 && lastDig <= 4) return n << 1; // If last digit is between // 5 to 9 then return 2*n + 1. else return (n << 1) + 1; } // Driver code static public void Main (string []args) { int n = 10; Console.WriteLine(findKthGoodNo(n)); } } // This code is contributed by Ajit. |
chevron_right
filter_none
PHP
<?php // PHP program to find n-th // Good number. // Function to find kth // good number. function findKthGoodNo($n) { // Find the last digit of n. $lastDig = $n % 10; // If last digit is between // 0 to 4 then return 2*n. if ($lastDig >= 0 && $lastDig <= 4) return $n << 1; // If last digit is between // 5 to 9 then return 2*n + 1. else return ($n << 1) + 1; } // Driver code $n = 10; echo(findKthGoodNo($n)); // This code is contributed by Ajit. ?> |
chevron_right
filter_none
Output:
20
Time Complexity: O(1)
Auxiliary Space: O(1)
Recommended Posts:
- Check whether product of digits at even places is divisible by sum of digits at odd place of a number
- Count of numbers between range having only non-zero digits whose sum of digits is N and number is divisible by M
- Maximize the given number by replacing a segment of digits with the alternate digits given
- Find the Largest number with given number of digits and sum of digits
- Find smallest number with given number of digits and sum of digits
- Minimum number of digits to be removed so that no two consecutive digits are same
- Smallest number with given sum of digits and sum of square of digits
- Number of digits in the nth number made of given four digits
- Build Lowest Number by Removing n digits from a given number
- Find maximum number that can be formed using digits of a given number
- Print a number strictly less than a given number such that all its digits are distinct.
- Number of times a number can be replaced by the sum of its digits until it only contains one digit
- Count number of digits after decimal on dividing a number
- Number of digits to be removed to make a number divisible by 3
- Find the smallest number whose digits multiply to a given number n
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.
- Count pairs in an array such that the absolute difference between them is ≥ K
- Partition an array of non-negative integers into two subsets such that average of both the subsets is equal
- Count Odd and Even numbers in a range from L to R
- Count pairs with given sum | Set 2
- Count of integers of length N and value less than K such that they contain digits only from the given set
- Count substrings that contain all vowels | SET 2
- Probability of distributing M items among X bags such that first bag contains N items
- Program to find the maximum difference between the index of any two different numbers
- Coin Change | BFS Approach
- Find two vertices of an isosceles triangle in which there is rectangle with opposite corners (0, 0) and (X, Y)
