``` #include <iostream> #include <cmath> using namespace std; int main() { int res=0; for(int x1=1;x1<=9;x1++) for(int x2=1;x2<=9;x2++) for(int y1=1;y1<=9;y1++) for(int y2=1;y2<=9;y2++) { if(x1==x2&&y1==y2) continue; double a=(x2*y2*1.0)/(x1*y1); double b=(x2*10+y2*1.0)/(x1*10+y1); if(a==b) res++; } cout<<res; return 0; } ```

直接暴力破解 ``` public class Main { public static void main(String[] args) { // 原等式为 (a/c) * (b/d) = ( a*10 + c/ b*10 + d ) // 但是直接使用除法的话有错误的可能性 // 可表示为 (a*b)*(c*10+d) = (a*10+b)*(c*d) int count = 0; for (int a = 1; a <= 9; a++) { for (int b = 1; b <= 9; b++) { for (int c = 1; c <= 9; c++) { // 分子分母相同 于是跳过 if (c == a) continue; for (int d = 1; d <= 9; d++) { // 分子分母相同 于是跳过 if (d == b) continue; if ((a * b) * (c * 10 + d) == (a * 10 + b) * (c * d)) count++; } } } } System.out.println(count); } } ```

暴力😄 ```c++ #include <cstdio> #include <vector> using namespace std; int main() { int res = 0; for (double a1 = 1; a1 <= 9; ++a1) { for (double a2 = 1; a2 <= 9; ++a2) { for (double b1 = 1; b1 <= 9; ++b1) { for (double b2 = 1; b2 <= 9; ++b2) { if (a1 == a2 || b1 == b2) continue; if ((double)a1/a2 * b1/b2 == (double)((a1 * 10) + b1)/((a2 * 10) + b2)) ++res; } } } } printf("%d\n", res); return 0; } ```

```cpp bool st[15]; double num[15]; int cnt = 0; void dfs(int x) { if (x > 4) { if (num[1] != num[2] and num[3] != num[4]) { if (num[1] * num[3] * (num[2] * 10 + num[4]) == num[2] * num[4] * (num[1] * 10 + num[3])) cnt++; } return; } for (int i = 1; i <= 9; i++) { num[x] = i; dfs(x + 1); } } void solve() { dfs(1); cout << cnt << endl; } ```

``` #include<iostream> #include<cstring> #include<algorithm> using namespace std; #define N 4 int cnt; int path[N]; bool vis[N]; bool check(int a,int b,int c,int d) { if(a==b&&c==d)return false; if(a*c*(10*b+d)==b*d*(10*a+c))return true; return false; } void dfs(int u) { if(u==4) { if(check(path[0],path[1],path[2],path[3])) { cnt++; for(int i=0;i<4;i++)cout<<path[i]<<" "; puts(""); } return ; } for(int i=1;i<=9;i++) { path[u]=i; dfs(u+1); } } int main() { dfs(0); cout<<cnt<<endl; return 0; } ```