51 lines
983 B
C++
51 lines
983 B
C++
#include <bits/stdc++.h>
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using namespace std;
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const int N = 1e5 + 10;
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const int WIDTH = 4; // 压4位
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const int BASE = 10000; // 基数为10000
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int a[N], al;
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int b;
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// 字符串转压位数组（逆序存储）
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void str2num(string s, int c[], int &cl) {
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cl = 0;
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for (int i = s.length() - 1; i >= 0; i -= WIDTH) {
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int v = 0;
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int st = max(i - WIDTH + 1, 0); // 最后一组可能不够4个长度
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for (int j = st; j <= i; j++)
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v = v * 10 + (s[j] - '0');
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c[cl++] = v;
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}
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}
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// 高精度乘以低精度
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void mul(int a[], int &al, int b) {
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int t = 0;
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for (int i = 0; i < al; i++) {
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t += a[i] * b;
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a[i] = t % BASE;
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t /= BASE;
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}
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if (t)
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a[al++] = t;
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while (al > 1 && a[al - 1] == 0)
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al--;
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}
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int main() {
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string x;
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cin >> x >> b;
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str2num(x, a, al);
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mul(a, al, b);
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printf("%d", a[al - 1]);
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for (int i = al - 2; i >= 0; i--)
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printf("%04d", a[i]);
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return 0;
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} |