Submission #4567381

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;

const int N = 1e6 + 5, mod = 998244353;

int n, m, ans, fac[N], inv[N];

inline int mul(int a, int b) { 
    return (LL) a * b % mod; 
}
inline void sub(int &a, int b) {
    a -= b; if(a < 0) a += mod;
}
inline int Pow(int a, int b = mod - 2) {
    int res = 1;
    for(; b; b >>= 1, a = mul(a, a))
        if(b & 1) res = mul(res, a);
    return res;
}
inline void init(int n) {
    inv[0] = fac[0] = 1;
    for(int i = 1; i <= n; ++i)
        fac[i] = mul(fac[i - 1], i);
    inv[n] = Pow(fac[n]);
    for(int i = n - 1; i; --i)
        inv[i] = mul(inv[i + 1], i + 1);
}
inline int C(int n, int m) {
    if(n < m || n < 0 || m < 0) return 0;
    return mul(fac[n], mul(inv[m], inv[n - m]));
}
int main() {
    cin >> n >> m;
    if(n > m) swap(n, m);
    init(n + m);
    ans = mul(C(n + m, n), n);
    for(int i = 1; i <= n; ++i) 
        sub(ans, mul(C(n + m - i * 2, n - i), C(i * 2 - 1, i)));
    ans = mul(ans, Pow(C(n + m, n)));
    ans = (n + m) - ans;
    printf("%d\n", (ans % mod + mod) % mod);
    return 0;
}

Submission Info

Judge Result