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47 lines
1.0 KiB
47 lines
1.0 KiB
#include <bits/stdc++.h>
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using namespace std;
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vector<int> add(vector<int> A, vector<int> B) {
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if (A.size() < B.size()) swap(A, B);
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vector<int> C;
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int t = 0;
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for (int i = 0; i < A.size(); i++) {
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t += A[i];
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if (i < B.size()) t += B[i];
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C.push_back(t % 10);
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t /= 10;
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}
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if (t) C.push_back(t);
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return C;
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}
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vector<int> mul(vector<int> A, int b) {
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vector<int> C;
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int t = 0;
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// 8899 * 2 = 17798
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for (int i = 0; i < A.size() || t; i++) {
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if (i < A.size()) t += A[i] * b;
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C.push_back(t % 10);
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t /= 10;
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}
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while (C.size() > 1 && C.back() == 0) C.pop_back();
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return C;
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}
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int main() {
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int n;
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cin >> n;
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vector<int> F, RES;
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//初始化
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RES.push_back(0);
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F.push_back(1);
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for (int i = 1; i <= n; i++) { //
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F = mul(F, i);
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RES = add(RES, F);
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}
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//倒序输出
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for (int i = RES.size() - 1; i >= 0; i--)
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printf("%d", RES[i]);
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return 0;
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} |