C++ program to check we can buy product with given money or not

Suppose we have a number N. A cake seller is selling cakes with 40 rupees, and doughnuts with 70 rupees each. We have to check whether we can buy some of them with exactly N rupees or not.

So, if the input is like N = 110, then the output will be True, because 40 + 70 = 110.

To solve this, we will follow these steps −

o := false
Define a function dfs(), this will take i,
if i > n, then:
   return false
if i is same as n, then:
   return true
if dfs(i + 40), then:
   return true
return dfs(i + 70)
From the main method, do the following
n := N
o := dfs(0)
return o


Let us see the following implementation to get better understanding −

#include <bits/stdc++.h>
using namespace std;
int n;
bool o = false;

bool dfs(int i) {
   if (i > n)
      return false;
   if (i == n)
      return true;
   if (dfs(i + 40))
      return true;
   return dfs(i + 70);
bool solve(int N) {
   n = N;
   o = dfs(0);
   return o;
int main(){
   int N = 110;
   cout << solve(N) << endl;