【学习笔记】hdu1042（高精度乘法）

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原题链接：http://acm.hdu.edu.cn/showproblem.php?pid=1049

代码：

#include <cstdio> #include <cstring>#include <malloc.h> #include <iostream>using namespace std;void intToArray(int num, char* a){int i = 0, len;int t;while (num){a[i++] = num % 10 + '0';num /= 10;}len = i;for (i = 0; i < len / 2; i++) {t = a[i];a[i] = a[len - i - 1];a[len - i - 1] = t;}a[len] = 0;}  void multiply(char* a, char* b, char* c) {      int i, j, ca, cb, * s;ca = strlen(a);     cb = strlen(b);      s = (int*)malloc(sizeof(int)*(ca+cb));     for (i = 0; i < ca + cb; i++)      s[i] = 0;      for (i = 0; i < ca; i++)      for (j = 0; j < cb; j++) s[i+j+1] += (a[i]-'0')*(b[j]-'0');     for (i = ca+cb-1; i >= 0; i--)      if (s[i] >= 10)      {          s[i-1] += s[i] / 10;          s[i] %= 10;         }     i = 0;      while (s[i]==0)      i++;      for (j = 0; i < ca + cb; i++, j++)      c[j] = s[i] + '0';     c[j] = '\0';     free(s); }int main(){int n, i;char ans[40000],b[10];while(~scanf("%d",&n)){ans[0] = '1'; ans[1] = 0;for (i = 1; i <= n; i++){intToArray(i,b);multiply(ans,b,ans);}cout << ans << endl;}return 0;}

其中multiply函数是个很有用的高精度乘法.

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