等边三角形

有如下一个题目：

我就直接for循环套，暴力求解。

#include <bits/stdc++.h>
using namespace std;
#define test cout<<"***"<<endl
int n;
int an[15];
int main(){
    cin>>n;
    int cnt = 0;
    memset(an,0,sizeof(an));
    int a,b,c,d,e,f,g,h,i;
    for(int i1=1;i1<=9;i1++){
        // test;
        a = i1;
        an[i1] = 1;
        for(int j=i1+1;j<=9;j++){
            f = j;
            an[j] = 1;
            for(int k=j+1;k<=9;k++){
                i = k;
                an[k] = 1;
                for(int p = 1;p<=9;p++){
                    if(an[p]==0){
                        b = p;
                        an[p] = 1;
                        for(int p1 = b;p1<=9;p1++){
                            if(an[p1]==0){
                                d = p1;
                                an[p1] = 1;
                                for(int p2=1;p2<=9;p2++){
                                    if(an[p2]==0){
                                        c = p2;
                                        an[p2] = 1;
                                        for(int p3 = c;p3<=9;p3++){
                                            if(an[p3]==0){
                                                e = p3;
                                                an[p3] = 1;
                                                for(int p4 =1;p4<=9;p4++){
                                                    if(an[p4]==0){
                                                        g = p4;
                                                        an[p4] = 1;
                                                        for(int p5 =g;p5<=9;p5++){
                                                            if(an[p5]==0){
                                                                h = p5;
                                                                an[p5]= 1;
                                                                int x=a+b+d+f;
                                                                int y=f+g+h+i;
                                                                int z=i+e+c+a;
                                                                if(x==y&&y==z&&x==n){
                                                                    cnt++;
                                                                //    cout<<a<<" "<<b<<" "<<c<<" "<<d<<" "<<e<<" "<<f<<" "<<g<<" "<<h<<" "<<i<<endl;
                                                                }
                                                                an[p5]=0;
                                                            }
                                                        }
                                                        an[p4] = 0;
                                                    }
                                                }
                                                an[p3] = 0;
                                            }
                                        }
                                        an[p2] = 0;
                                    }
                                }
                                an[p1] = 0;
                            }
                        }
                        an[p] = 0;
                    }
                }
                an[k] = 0;
            }
            an[j] = 0;
        }
        an[i1]=0;
    }
    if(cnt)
        cout<<cnt<<endl;
    else
        cout<<"No"<<endl;
    return 0;
}

下面是后台测试数据（过了说明代码就行了）：

23 2
18 No
19 4
20 6
21 4