Largest number less than N with digit sum greater than the digit sum of N

Given an integer N, the task is to find the greatest number less than N such that the sum of its digits is greater than the sum of the digits of N. If the condition isn’t satisfied for any number then print -1.

Examples:

Input: N = 100
Output: 99
99 is the largest number less than 100 sum of whose digits is greater than the sum of the digits of 100

Input: N = 49
Output: -1



Approach: Start a loop from N-1 to 1 and check whether the sum of the digits of any number is greater than the sum of the digits of N. The first number that satisfies the condition is the required number.

Below is the implementation of the above approach:

C++

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// C++ implementation of the approach
#include <iostream>
using namespace std;
  
// Function to return the sum of the digits of n
int sumOfDigits(int n)
{
    int res = 0;
  
    // Loop for each digit of the number
    while (n > 0) {
        res += n % 10;
        n /= 10;
    }
  
    return res;
}
  
// Function to return the greatest
// number less than n such that
// the sum of its digits is greater
// than the sum of the digits of n
int findNumber(int n)
{
  
    // Starting from n-1
    int i = n - 1;
  
    // Check until 1
    while (i > 0) {
  
        // If i satisfies the given condition
        if (sumOfDigits(i) > sumOfDigits(n))
            return i;
        i--;
    }
  
    // If the condition is not satisfied
    return -1;
}
  
// Driver code
int main()
{
    int n = 824;
    cout << findNumber(n);
  
    return 0;
}

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Java

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//Java implementation of the approach
  
import java.io.*;
  
class GFG {
    // Function to return the sum of the digits of n
static int sumOfDigits(int n)
{
    int res = 0;
  
    // Loop for each digit of the number
    while (n > 0) {
        res += n % 10;
        n /= 10;
    }
  
    return res;
}
  
// Function to return the greatest
// number less than n such that
// the sum of its digits is greater
// than the sum of the digits of n
static int findNumber(int n)
{
  
    // Starting from n-1
    int i = n - 1;
  
    // Check until 1
    while (i > 0) {
  
        // If i satisfies the given condition
        if (sumOfDigits(i) > sumOfDigits(n))
            return i;
        i--;
    }
  
    // If the condition is not satisfied
    return -1;
}
  
// Driver code
    public static void main (String[] args) {
  
    int n = 824;
    System.out.println (findNumber(n));
    }
//This code is contributed by akt_mit    
}

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Python3

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# Python3 implementation of the approach
  
# Function to return the sum 
# of the digits of n
def sumOfDigits(n) :
  
    res = 0;
  
    # Loop for each digit of the number
    while (n > 0) :
        res += n % 10
        n /= 10
  
    return res;
  
# Function to return the greatest
# number less than n such that
# the sum of its digits is greater
# than the sum of the digits of n
def findNumber(n) :
  
    # Starting from n-1
    i = n - 1;
  
    # Check until 1
    while (i > 0) :
  
        # If i satisfies the given condition
        if (sumOfDigits(i) > sumOfDigits(n)) :
            return i
              
        i -= 1
  
    # If the condition is not satisfied
    return -1;
  
# Driver code
if __name__ == "__main__" :
      
    n = 824;
    print(findNumber(n))
  
# This code is contributed by Ryuga

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C#

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// C# implementation of the approach
using System;
  
class GFG
{
// Function to return the sum 
// of the digits of n
static int sumOfDigits(int n)
{
    int res = 0;
  
    // Loop for each digit of 
    // the number
    while (n > 0) 
    {
        res += n % 10;
        n /= 10;
    }
  
    return res;
}
  
// Function to return the greatest
// number less than n such that
// the sum of its digits is greater
// than the sum of the digits of n
static int findNumber(int n)
{
  
    // Starting from n-1
    int i = n - 1;
  
    // Check until 1
    while (i > 0)
    {
  
        // If i satisfies the given condition
        if (sumOfDigits(i) > sumOfDigits(n))
            return i;
        i--;
    }
  
    // If the condition is
    // not satisfied
    return -1;
}
  
// Driver code
static public void Main ()
{
    int n = 824;
    Console.WriteLine (findNumber(n));
}
}
  
// This code is contributed by @Tushil

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PHP

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<?php
//PHP implementation of the approach
  
// Function to return the sum of 
// the digits of n
function sumOfDigits($n)
{
    $res = 0;
  
    // Loop for each digit of the number
    while ($n > 0) 
    {
        $res += $n % 10;
        $n /= 10;
    }
  
    return $res;
}
  
// Function to return the greatest
// number less than n such that
// the sum of its digits is greater
// than the sum of the digits of n
function findNumber($n)
{
  
    // Starting from n-1
    $i = $n - 1;
  
    // Check until 1
    while ($i > 0) 
    {
  
        // If i satisfies the given condition
        if (sumOfDigits($i) > sumOfDigits($n))
            return $i;
        $i--;
    }
  
    // If the condition is not satisfied
    return -1;
}
  
// Driver code
$n = 824;
  
echo findNumber($n);
      
// This code is contributed by Mukul singh
?>

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Output:

819


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