Form N by adding 1 or 2 in minimum number of operations X where X is divisible by M

Given a number N, the task is to form N (from 0) by adding 1 or 2 in the minimum number of operations X such that X is divisible by M.

Examples:

Input: N = 10, M = 2
Output: X = 6
Explanation:
Taken operations are 2 2 2 2 1 1
X = 6 which is divisible by 2

Input: N = 17, M = 4
Output: 8

Approach:



  • As we can take either 1 or 2 steps at a time, so we can say that minimum no. of steps taken is n/2, and the maximum no. of steps is n, irrespective of that the no. of steps are divisible by m.
  • So we have to count n/2 steps to get a minimum number of steps. Now if n is even, then a minimum number of steps will be n/2, but if it is odd, then it will be n/2+1, irrespective of that the no. of steps are divisible by m. To make minimum steps of a multiple of m we can do floor((minumum_steps + m – 1)/m) * m
  • Also if n is less than m, then it is not possible to find the minimum number of steps, and in that case, we will return -1.

Below is the implementation of above approach:

C++

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// C++ program to find minimum
// number of steps to cover distance x
  
#include <bits/stdc++.h>
using namespace std;
  
// Function to calculate the minimum number of steps required
// total steps taken is divisible
// by m and only 1 or 2 steps can be taken at // a time
int minsteps(int n, int m)
{
  
    // If m > n ans is -1
    if (m > n) {
        return -1;
    }
    // else discussed above approach
    else {
        return ((n + 1) / 2 + m - 1) / m * m;
    }
}
  
// Driver code
int main()
{
    int n = 17, m = 4;
    int ans = minsteps(n, m);
    cout << ans << '\n';
  
    return 0;
}

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Java

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// Java program to find minimum 
// number of steps to cover distance x 
class GFG 
{
  
    // Function to calculate the 
    // minimum number of steps required 
    // total steps taken is divisible 
    // by m and only 1 or 2 steps can be
    // taken at // a time 
    static int minsteps(int n, int m) 
    
      
        // If m > n ans is -1 
        if (m > n) 
        {
            return -1
        
          
        // else discussed above approach 
        else 
        
            return ((n + 1) / 2 + m - 1) / m * m; 
        
    
      
    // Driver code 
    public static void main (String[] args)
    
        int n = 17, m = 4
        int ans = minsteps(n, m); 
        System.out.println(ans); 
    
}
  
// This code is contributed by AnkitRai01

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Python3

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# Python3 program to find minimum
# number of steps to cover distance x
  
# Function to calculate the minimum number of 
# steps required total steps taken is divisible
# by m and only 1 or 2 steps can be taken at a time
def minsteps(n, m):
  
    # If m > n ans is -1
    if (m > n):
        return -1
          
    # else discussed above approach
    else :
        return ((n + 1) // 2 + m - 1) // m * m;
  
# Driver code
n = 17
m = 4
ans = minsteps(n, m)
print(ans)
  
# This code is contributed by Mohit Kumar

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C#

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// C# program to find minimum 
// number of steps to cover distance x 
using System;
      
class GFG 
{
  
    // Function to calculate the 
    // minimum number of steps required 
    // total steps taken is divisible 
    // by m and only 1 or 2 steps can be
    // taken at // a time 
    static int minsteps(int n, int m) 
    
      
        // If m > n ans is -1 
        if (m > n) 
        {
            return -1; 
        
          
        // else discussed above approach 
        else
        
            return ((n + 1) / 2 + m - 1) / m * m; 
        
    
      
    // Driver code 
    public static void Main (String[] args)
    
        int n = 17, m = 4; 
        int ans = minsteps(n, m); 
        Console.WriteLine(ans); 
    
}
  
// This code is contributed by 29AjayKumar

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Output:

12

Time Cmplexity: O(1)

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