UVA 11076 Add Again——计数原理

注意先乘后除否则会有精度损失

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define OUT freopen("out.txt", "w", stdout)
using namespace std;
typedef long long ll;
const int maxn = 15;
const ll one[] = {0, 1, 11, 111, 1111, 11111, 111111, 1111111, 11111111, 111111111, 1111111111, 11111111111, 111111111111};
ll n, a[maxn];
ll cnt, val[maxn], num[maxn], sum;
int main() {
    //OUT;
    while (~scanf("%lld", &n) && n) {
        sum = 0;
        for (int i = 1; i <= n; i++) {
            scanf("%lld", &a[i]);
            sum += a[i];
        }
        sort(a + 1, a + 1 + n);
        memset(num, 0, sizeof(num));
        val[1] = a[1];
        num[1] = 1;
        cnt = 1;
        for (int i = 2; i <= n; i++) {
            if (a[i] != a[i - 1]) ++cnt;
            val[cnt] = a[i];
            num[cnt]++;
        }
        ll n1 = 1, n2 = 1;
        for (int i = 1; i <= n; i++) n1 *= i;
        for (int i = 1; i <= cnt; i++) {
            for (int j = 1; j <= num[i]; j++) n2 *= j;
        }
        ll k = n1 / n2;
        ll ans = sum * k / n * one[n];
        printf("%lld\n", ans);
    }
    return 0;
}