Teacher Yang's game

Link: https://www.nowcoder.com/acm/contest/116/B
Source: Niuke.com

Time limit: C/C++ 1 second, other languages ​​2 seconds
Space limit: C/C++ 32768K, other languages ​​65536K
64bit IO Format: %lld

Topic description

Mr. Yang played a game for the students and asked to use multiplication and subtraction to represent a number. He gave everyone 9 cards, and then reported a number, and asked everyone to express the number in the form of an expression.
100 can be expressed as this Form: 100 = 129*67-8543, can also be expressed as: 100 = 13*489-6257
Note: In the expression, the numbers 1~9 appear respectively and only once (excluding 0).
For expressions like this, 100 has 20 representations.
Question requirements:
Read a positive integer N (N<1000 * 1000) from the standard input, and the
program outputs all the numbers that the number is composed of numbers 1~9 without repetition or omission.
Note: It is not required to output every representation, only count how many representations there are!

Enter description:

a positive integer N

Output description:

How many representations are there for the output

Example 1

enter

100

output

20

Remark:

Note that there is only one multiplication and one subtraction, and the * sign is guaranteed to be in front of the -

#include<iostream>
using namespace std;
int n,ans=0;
bool fish [10];
int num[10];
void cal(int x,int y){
    int a=0,b=0,c=0;
    for(int i=0;i<=x;i++){
        a=a*10+num[i];
    }
    for(int i=x+1;i<=y;i++){
        b=b*10+num[i];
    }
    for(int i=y+1;i<9;i++){
        c=c*10+num[i];
    }
    if((a*b-c)==n)
        years++;
}
void solve(){
    for(int i=0;i<9;i++){
        for(int j=i+1;j<9;j++){
            cal(i,j);
        }
    }
}
void dfs(int d){
    if(d==9){
        solve();
        return;
    }
    for(int i=1;i<10;i++){
        if(!vis[i]){
            vis[i]=true;
            num[d]=i;
            dfs(d+1);
            show [i] = false;
        }
    }
}
int main(){
    cin>>n;
    dfs(0);
    cout<<ans<<endl;
return 0;
}

#include<iostream>
#include<algorithm>
using namespace std;
int n,ans=0;
bool fish [10];
int num[10];
void cal(int x,int y){
    int a=0,b=0,c=0;
    for(int i=0;i<=x;i++){
        a=a*10+num[i];
    }
    for(int i=x+1;i<=y;i++){
        b=b*10+num[i];
    }
    for(int i=y+1;i<9;i++){
        c=c*10+num[i];
    }
    if((a*b-c)==n)
        years++;
}
void solve(){
    for(int i=0;i<9;i++){
        for(int j=i+1;j<9;j++){
            cal(i,j);
        }
    }
}
int main(){
    cin>>n;
    for(int i=0;i<9;i++){
        num[i]=i+1;
    }
    int t=9*8*7*6*5*4*3*2*1-1;
    while(t--){
        next_permutation(num,num+9);
        solve();
    }
    cout<<ans<<endl;
return 0;
}