数的分解

要使其顺序无影响，j=i+1,k=j+1即可
顺序有影响，j=1,k=1即可

#include<bits/stdc++.h>
using namespace std;
const int N = 3e7+10;
const int Mod = 1e5;
int check(int i) {
  while(i) {
    if(i%10 == 2 || i%10 == 4) return 0;
    i /= 10;
  }
  return 1;
}
int main() {
  int n = 2019, sum = 0;
  for(int i = 1; i < n - 1; ++i) {
    if(!check(i)) continue;
    for(int j = i+1; j < n; ++j) {
      if(!check(j)) continue;
      for(int k = j+1; k <= n; ++k) {
        if(check(k)&&i + j + k == 2019)
          ++sum;
      }
    }
  }
  printf("%d\n", sum);
  return 0;
}