atcoder/abc185C (feedback from editorial)

Author: xirc

atcoder/abc185/C/main.cpp

@@ -1,52 +1,5 @@
 #include <bits/stdc++.h>
 
-template<uint64_t MOD = std::numeric_limits<uint64_t>::max()>
-class CombinationPascal {
-    size_t N;
-    std::vector<std::vector<uint64_t>> comb;
-
-public:
-    // Time: O(N^2)
-    CombinationPascal(
-        size_t const N = 1000
-    )
-    {
-        build(N);
-    }
-    // Time: O(N^2)
-    void build(size_t const N) {
-        this->N = N;
-        comb.assign(N + 1, std::vector<uint64_t>(N + 1, 0));
-        comb[0][0] = 1;
-        for (size_t n = 1; n <= N; ++n) {
-            comb[n][0] = 1;
-            for (size_t k = 1; k <= N; ++k) {
-                comb[n][k] = (comb[n-1][k-1] + comb[n-1][k]) % MOD;
-            }
-        }
-    }
-    // nCk
-    // n = [0,N], k = [0,n]
-    // Time: O(1)
-    uint64_t C(size_t const n, size_t const k) const {
-        if (k > n) throw std::out_of_range("k");
-        if (n > N) throw std::out_of_range("n");
-        return comb[n][k];
-    }
-    // nHk
-    // H(n,k) = C(n+k-1,k)
-    // n = [0,N-k+1], k = [0,N]
-    // Time: O(1)
-    uint64_t H(size_t const n, size_t const k) const {
-        if (n == 0 && k == 0) return 1;
-        return C(n+k-1,k);
-    }
-    // Time: O(1)
-    size_t size() const {
-        return N;
-    }
-};
-
 using namespace std;
 using ll = int64_t;
 using ff = long double;
@@ -58,8 +11,11 @@ int main() {
     int L;
     cin >> L;
 
-    CombinationPascal<> solver(300);
-    ll ans = solver.H(12, L-12);
+    ll ans = 1;
+    for (int i = 1; i <= 11; ++i) {
+        ans *= L- i;
+        ans /= i;
+    }
     cout << ans << endl;
 
     return 0;