1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
|
#include <bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
#define CLR(i,a) memset(i,a,sizeof(i))
#define fi first
#define se second
#define pb push_back
#define SZ(a) ((int) a.size())
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (int i = (a); i >= (b); --i)
#define getFro(vec) (vec.empty()?0:vec.front())
#define getBac(vec) (vec.empty()?0:vec.front())
#define debug(var) cerr << #var <<":"<<var<<"\n";
#define DEBUG(variable) \
do { \
std::cerr << #variable << ":"; \
for (const auto& elem : variable) { \
std::cerr << elem << " "; \
} \
std::cerr << "\n"; \
} while (0)
#define uniVec(var) \
do { \
sort(var.begin(),var.end());\
var.resize(unique(var.begin(),var.end())-var.begin());\
} while (0)
#define debugN(var,N) \
do{ \
std::cerr<<#var<<":"; \
FOR(i,1,N){ \
std::cerr<<var[i]<<" "; \
} \
std::cerr<<"\n"; \
}while(0)
#define debugMap(variable) \
do { \
std::cerr << #variable << ":\n"; \
for (const auto& pair : variable) { \
std::cerr << " " << pair.first << " => " << pair.second << "\n"; \
} \
std::cerr << std::endl; \
} while (0)
#define lson(var) (var<<1)
#define rson(var) ((var<<1)+1)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128;
typedef pair<ll,ll> pll;
typedef array<ll,3> arr;
typedef double DB;
typedef pair<DB,DB> pdd;
typedef pair<ll,bool> plb;
constexpr ll MAXN=static_cast<ll>(1e6)+10,INF=static_cast<ll>(1e18)+3;
constexpr ll mod=998244353;
constexpr double eps=1e-8;
ll N,M,K,T;
/*
*/
struct Comb{
vector<ll> frac,infrac;
int ln=1;
Comb(int n){
ln=n;
frac.resize(n+5,1);
infrac.resize(n+5,1);
for(int i=1;i<=ln;++i){
frac[i]=frac[i-1]*i;
frac[i]%=mod;
}
for(int i=1;i<=ln;++i){
infrac[i]=binpow(frac[i],mod-2);
}
}
inline ll binpow(ll a,ll k){
ll res=1;
while(k){
if(k&1) res*=a;
a*=a;
a%=mod;
res%=mod;
k>>=1;
}
return res;
}
inline ll C(ll n,ll k){
ll res=frac[n]*infrac[n-k];
res%=mod;
res*=infrac[k];
res%=mod;
return res;
}
inline ll P(ll n,ll k){
ll res=frac[n]*infrac[n-k];
res%=mod;
return res;
}
};
inline void solve(){
ll a,b,c,d;
cin>>a>>b>>c>>d;
N=a+b+c+d;
Comb comb(a+b+c+d);
// 显然是要枚举水果的边界
ll ans=0;
FOR(i,a,a+b){
// 在i-1个空位中选a-1个空位(因为第i个位置已经钦定了A（苹果）)
ll res=comb.C(i-1,a-1);
res*=comb.C(N-i,c);
res%=mod;
ans+=res;
}
ans%=mod;
if(ans<0) ans+=mod;
cout<<ans<<"\n";
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
// cin>>T;
// while(T--){
// solve();
// }
solve();
return 0;
}
/*
AC
https://atcoder.jp/contests/abc405/submissions/66027443
*/
|
