new file: P16807.cpp

P16807.cpp

@@ -0,0 +1,39 @@
+#include <bits/stdc++.h>
+using namespace std;
+const long long mod = 998244353;
+long long n, m; // 1e5
+long long jc[200005];
+long long qpow(long long a, long long b)
+{
+    if (b == 0)
+        return 1ll;
+    long long res = 1;
+    while (b > 0)
+    {
+        if (b & 1)
+            res = a * res % mod;
+        a = a * a % mod, b /= 2;
+    }
+    return res;
+}
+long long ni(long long a)
+{
+    return qpow(a, mod - 2);
+}
+long long C(long long a, long long b)
+{
+    return ((jc[a] * ni(jc[a - b])) % mod * ni(jc[b])) % mod;
+}
+signed main()
+{
+    scanf("%lld%lld", &n, &m);
+    long long now = 1;
+    jc[0] = 1;
+    for (long long i = 1; i <= m + n; ++i)
+        now = now * i % mod, jc[i] = now;
+    long long ans = (C(n + m, m) - C(n + m, m - 1));
+    while (ans < 0)
+        ans += mod;
+    printf("%lld\n", ans % mod);
+    return 0;
+}