'commit'

GESP/Mkx/jiecheng-simple.cpp

@@ -0,0 +1,70 @@
+#include <bits/stdc++.h>
+using namespace std;
+const int N = 1e5 + 10;
+int a[N], al;
+int b[N], bl;
+
+void mul(int a[], int &al, int b[], int &bl) {
+  int t = 0;
+  int c[N] = {0};
+  for (int i = 0; i < al; i++)
+    for (int j = 0; j < bl; j++)
+      c[i + j] += a[i] * b[j];
+  al += bl;
+  for (int i = 0; i < al; i++) {
+    t += c[i];
+    a[i] = t % 10;
+    t /= 10;
+  }
+  while (al > 0 && a[al - 1] == 0)
+    al--;
+}
+void jiecheng(int x) {
+  a[0] = 1;
+  al = 1;
+
+  for (int i = 2; i <= x; i++) {
+    int t = i;
+    bl = 0;
+    while (t > 0) {
+      b[bl++] = t % 10;
+      t /= 10;
+    }
+    mul(a, al, b, bl);
+  }
+}
+
+void add(int a[], int &al, int b[], int &bl) {
+  int t = 0;
+  al = max(al, bl);
+  for (int i = 0; i < al; i++) {
+    t += a[i] + b[i];
+    a[i] = t % 10;
+    t /= 10;
+  }
+  if (t)
+    a[al++] = 1;
+  while (al > 0 && a[al - 1] == 0)
+    al--;
+}
+
+int main() {
+  int n;
+  cin >> n; // 读入n
+
+  int sum[N] = {0}; // 存储总和
+  int suml = 0;     // 总和的长度
+
+  for (int i = 1; i <= n; i++) {
+    jiecheng(i);           // 计算i的阶乘，结果存在a数组中
+    add(sum, suml, a, al); // 将a数组的结果加到sum数组中
+  }
+
+  // 从高位到低位输出结果
+  for (int i = suml - 1; i >= 0; i--) {
+    cout << sum[i];
+  }
+  cout << endl;
+
+  return 0;
+}