Codeforces 300C Beautiful Numbers 【组合数学】
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题目链接:Codeforces 300C Beautiful Numbers
题意:给定两个数
思路:我们枚举
#include <iostream>#include <cstdio>#include <cstring>#include <cstdlib>#include <cmath>#include <algorithm>#include <vector>#include <queue>#include <map>#include <stack>#define PI acos(-1.0)#define CLR(a, b) memset(a, (b), sizeof(a))#define fi first#define se second#define ll o<<1#define rr o<<1|1using namespace std;typedef long long LL;typedef pair<int, int> pii;const int MAXN = 1e6 + 1;const int pN = 1e6;// <= 10^7const int INF = 0x3f3f3f3f;const int MOD = 1e9 + 7;void add(LL &x, LL y) { x += y; x %= MOD; }LL fac[MAXN];void getfac(){ fac[0] = 1 % MOD; for(LL i = 1; i < MAXN; i++) fac[i] = fac[i-1] * i % MOD;}LL Pow(LL a, LL n){ LL ans = 1; while(n) { if(n & 1) ans = ans * a % MOD; a = a * a % MOD; n >>= 1; } return ans;}int n, a, b;bool judge(int v) { while(v) { if(v % 10 != a && v % 10 != b) return false; v /= 10; } return true;}LL C(LL n, LL m) { return fac[n] * Pow(fac[m], MOD-2) % MOD * Pow(fac[n-m], MOD-2) % MOD;}int main(){ getfac(); cin >> a >> b >> n; LL ans = 0; for(int i = 0; i <= n; i++) { int v = a * i + b * (n-i); if(judge(v)) { add(ans, C(n, i)); } } cout << ans << endl; return 0;}
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