时间限制: 1000 ms 空间限制: 262144 KB
题目描述
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输入
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输出
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样例输入
样例输出
数据范围限制
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代码
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| #include<bits/stdc++.h> #define ll long long #define maxn 2010 #define mod 998244353 using namespace std; ll f[maxn][maxn]; int main() { freopen("map.in", "r", stdin); freopen("map.out", "w", stdout); int n, s1 = 0, s2 = 0; scanf("%d", &n); for (int i = 1; i <= n; i++) { int x; scanf("%d", &x); if (x == 1) s1++; else s2++; } f[0][0] = 1; for (int tot = 0; tot <= n; tot++) for (int i = tot; i >= 0; i--) { int j = tot - i; if (j < 0) continue; if (j == 0 && i) f[i + 1][j] = (f[i + 1][j] + f[i - 1][j] * i % mod) % mod; if (i >= 2) { ll tmp = f[i - 2][j] * ((ll)i * (i - 1) / 2 % mod) % mod; f[i][j + 1] = (f[i][j + 1] + tmp) % mod; } if (j >= 2) { ll tmp = f[i + 2][j - 2] * ((ll)j * (j - 1) / 2 % mod) % mod; f[i][j + 1] = (f[i][j + 1] + tmp) % mod; } if (i && j) { ll tmp = f[i][j - 1] * i % mod * j % mod; f[i][j + 1] = (f[i][j + 1] + tmp) % mod; } } printf("%lld\n", f[s1][s2]); return 0; }
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