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  1. #include <string>
  2. #include <iostream>
  3.  
  4. using namespace std;
  5.  
  6.     void mul(int int1[], int num2, int cur[], int n1) {
  7.         int inc = 0;
  8.  
  9.         for (int i = 0; i < n1; i ++) {
  10.             inc += int1[i] * num2;
  11.             cur[i] = inc % 10;
  12.             inc /= 10;
  13.         }
  14.  
  15.         cur[n1] = inc;
  16.     }
  17.  
  18.     void add(int ret[], int cur[], int n1, int shift) {
  19.         int inc = 0;
  20.  
  21.         for (int i = 0; i < n1+1; i ++) {
  22.             inc += ret[i+shift] + cur[i];
  23.             ret[i+shift] = inc % 10;
  24.             inc /= 10;
  25.         }
  26.     }
  27.  
  28.     string multiply(string num1, string num2) {
  29.         int n1 = num1.length();
  30.         int n2 = num2.length();
  31.  
  32.         int int1[n1];
  33.         int cur[n1+1];
  34.         int ret[n1+n2];
  35.  
  36.         for (int i = 0; i < n1; i ++) {
  37.             int1[i] = num1[n1-i-1]-'0';
  38.         }
  39.         cur[n1] = 0;
  40.  
  41.         for (int i = 0; i < n1+n2; i ++) {
  42.             ret[i] = 0;
  43.         }
  44.  
  45.  
  46.         for (int i = 0; i < n2; i ++) {
  47.             mul(int1, num2[n2-i-1]-'0', cur, n1);
  48.             add(ret, cur, n1, i);
  49.         }
  50.  
  51.         int len = 0;
  52.  
  53.         for (int i = n1+n2-1; i >= 0; i --) {
  54.             if (ret[i] != 0) {
  55.                 len = i;
  56.                 break;
  57.             }
  58.         }
  59.  
  60.         char chars[len+1];
  61.  
  62.         for (int i = 0; i < len+1; i ++) {
  63.             chars[len-i] = ret[i] + '0';
  64.         }
  65.  
  66.         return string(chars, len+1);
  67.     }
  68.  
  69.  
  70. int main (int argc, char* argv[]) {
  71.  
  72.     cout << multiply("10", "10") << endl;
  73.  
  74.     return 0;
  75. }
Success #stdin #stdout 0s 3428KB
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https://ideone.com/y3ZTIs
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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