题意:给出n个数,其中有一个数会出现两次,其余数只出现一次,问不同长度且不同的子串的数量。取模1e9+7
思路:组合求出所有情况,减去重复情况,注意用逆元即可
/** @Date : 2017-07-06 09:56:44 * @FileName: atcoder077 D 组合.cpp * @Platform: Windows * @Author : Lweleth (SoungEarlf@gmail.com) * @Link : https://github.com/ * @Version : $Id$ */ #include <bits/stdc++.h> #define LL long long #define PII pair #define MP(x, y) make_pair((x),(y)) #define fi first #define se second #define PB(x) push_back((x)) #define MMG(x) memset((x), -1,sizeof(x)) #define MMF(x) memset((x),0,sizeof(x)) #define MMI(x) memset((x), INF, sizeof(x)) using namespace std; const int INF = 0x3f3f3f3f; const int N = 1e5+20; const double eps = 1e-8; const LL mod = 1e9 + 7; LL a[N]; LL inv[N]; LL fa[N]; LL n; void init() { fa[0] = fa[1] = 1; inv[1] = 1; for(LL i = 2; i < N; i++) { fa[i] = fa[i-1] * i % mod; inv[i] = (mod - mod / i) * inv[mod % i] % mod; } inv[0] = 1; for(int i = 1; i < N; i++) (inv[i] *= inv[i - 1]) %= mod; } LL C(LL n, LL k) { LL ans = 0; if(k > n) return ans; ans = ((fa[n] * inv[k] % mod) * inv[n - k]) % mod; return ans; } int main() { init(); while(cin >> n) { map<LL, int>q; LL p = 0; for(int i = 1; i <= n + 1; i++) { scanf("%lld", a + i); if(!q[a[i]]) q[a[i]] = i; else p = i; } for(int i = 0; i <= n; i++) { LL ans = 0; ans = (ans + C(n + 1, i + 1)) % mod; ans = (ans - C(n - p + q[a[p]], i)) % mod; while(ans < 0) ans += mod; printf("%lld ", ans); } } return 0; }