洛谷 - P2089 - 烤鸡 - dfs

#include<bits/stdc++.h>
using namespace std;
#define ll long long

int n;

set<ll> ans;

void dfs(int i,int c,int res,ll sum){
    res-=c;
    sum=sum*10+c;
    if(res<0)
        return;
    if((10-i)>res||(10-i)*3<res)
        return;
    if(i==10){
        if(res!=0)
            return;
        else{
            ans.insert(sum);
        }
    }
    else{
        dfs(i+1,1,res,sum);
        dfs(i+1,2,res,sum);
        dfs(i+1,3,res,sum);
    }
}

int main(){
    scanf("%d",&n);
    dfs(1,1,n,0);
    dfs(1,2,n,0);
    dfs(1,3,n,0);

    printf("%d\n",ans.size());
    for(auto i:ans){
        //cout<<i<<endl;;
        ll t=i;

        stack<int> s;
        while(t){
            s.push(t%10);
            t/=10;
        }

        while(!s.empty()){
            printf("%d",s.top());
            s.pop();
            if(s.empty())
                printf("\n");
            else
                printf(" ");
        }
    }
}