leetcode.com/problems/multiply-strings

main.cpp

#include <iostream>
#include <vector>
#include <ranges>
#include <algorithm>

using namespace std;

class Solution {
public:
    string m2(string num1, int multiplier, int zeros) {
      string out;
      while(zeros > 0) {
        out.push_back('0');
        zeros--;
      }
      int l1 = num1.length();
      int carry = 0;
      while(l1 > 0) {
        l1 --;
        int v1 = num1[l1] - '0';
        int v2 = multiplier * v1 + carry;
        if(v2 > 9) {
          carry = v2 / 10;
          v2 = v2 % 10;
        } else {
          carry = 0;
        }
        out.insert(out.begin(), v2 + '0');
      }
      if(carry > 0) {
        out.insert(out.begin(), carry + '0');
      }
      return out;
    }

    string multiply(string num1, string num2) {
      int l1 = num1.length();
      string out = "0";
      int zero = 0;
      while(l1 > 0) {
        l1 --;
        int multiplier = l1 >= 0 ? num1[l1] - '0' : 1;  
        string result = m2(num2, multiplier, zero);
        zero ++;
        out = add(result, out);
      }
      // Check for all zeros
      int i=0;
      auto allZero = false;
      while(i<out.length()) {
        if(out[i] != '0') {
          return out;
        }
        i++;
      }
      return "0";
    }

    string add(string num1, string num2) {
      int l1 = num1.length();
      int l2 = num2.length();
      string out = "";
      int carry = 0;
      while(l1 > 0 || l2 > 0) {
        l1 --;
        l2 --;
        int v1 = l1 >= 0 ? num1[l1] - '0' : 0;
        int v2 = l2 >= 0 ? num2[l2] - '0' : 0;
        int v3 = v1 + v2 + carry;
        if(v3 > 9) {
          carry = v3 / 10;
          v3 -= 10;
        } else {
          carry = 0;
        }
        out.insert(out.begin(), v3 + '0');
      }
      if(carry > 0) {
        out.insert(out.begin(), carry + '0');
      }
      return out;
    }
};

int main(int, char** args) {

  auto m = new Solution();
  auto r1 = m->multiply("123", "456");
  auto r2 = m->multiply("923", "956");
  auto r3 = m->multiply("9133", "0");

  cout << "multiply 123 and 456 should be 56088 it is " << r1 << "\n";
  cout << "multiply 923 and 956 should be 882388 it is " << r2 << "\n";
  cout << "multiply 9133 and 0 should be 0 it is " << r3 << "\n";

  delete m;
}