148 lines
3.7 KiB
C++
148 lines
3.7 KiB
C++
// Source : https://oj.leetcode.com/problems/multiply-strings/
|
|
// Author : Hao Chen
|
|
// Date : 2014-07-18
|
|
|
|
/**********************************************************************************
|
|
*
|
|
* Given two numbers represented as strings, return multiplication of the numbers as a string.
|
|
*
|
|
* Note: The numbers can be arbitrarily large and are non-negative.
|
|
*
|
|
**********************************************************************************/
|
|
|
|
#include <iostream>
|
|
#include <string>
|
|
using namespace std;
|
|
|
|
string multiply(string& num, char ch){
|
|
int n = ch - '0';
|
|
string s;
|
|
int carry = 0;
|
|
int x;
|
|
for(int i=num.size()-1; i>=0; i--){
|
|
x = (num[i]-'0') * n + carry;
|
|
carry = x/10;
|
|
s.insert(s.begin(), x%10+'0');
|
|
}
|
|
if (carry>0) {
|
|
s.insert(s.begin(), carry+'0');
|
|
}
|
|
return s;
|
|
}
|
|
|
|
string strPlus(string& num1, string& num2) {
|
|
string s;
|
|
int carry=0;
|
|
int x;
|
|
int n1 = num1.size();
|
|
int n2 = num2.size();
|
|
|
|
int i, j;
|
|
for(i=n1-1, j=n2-1; i>=0 || j>=0; i--, j--){
|
|
int x1 = i>=0 ? num1[i]-'0' : 0;
|
|
int x2 = j>=0 ? num2[j]-'0' : 0;
|
|
x = x1 + x2 + carry;
|
|
carry = x/10;
|
|
s.insert(s.begin(), x%10+'0');
|
|
}
|
|
if (carry>0) {
|
|
s.insert(s.begin(), carry+'0');
|
|
}
|
|
return s;
|
|
}
|
|
|
|
string multiply(string num1, string num2) {
|
|
|
|
if (num1.size()<=0 || num2.size()<=0) return "";
|
|
|
|
int shift=0;
|
|
string result="0";
|
|
for (int i=num1.size()-1; i>=0; i--) {
|
|
string s = multiply(num2, num1[i]);
|
|
for(int j=0; j<shift; j++){
|
|
s.insert(s.end(), '0');
|
|
}
|
|
result = strPlus(result, s);
|
|
shift++;
|
|
}
|
|
//check if it is zero
|
|
if (result[0]=='0') return "0";
|
|
return result;
|
|
}
|
|
|
|
|
|
/**********************************************************************************
|
|
* Another implementation
|
|
**********************************************************************************/
|
|
|
|
class Solution {
|
|
public:
|
|
|
|
string strPlus(string& num1, string& num2) {
|
|
if (num1.size()==0) return num2;
|
|
if (num2.size()==0) return num1;
|
|
|
|
if ( num1.size() < num2.size() ) {
|
|
swap(num1, num2);
|
|
}
|
|
|
|
string s;
|
|
int carry=0;
|
|
int x;
|
|
for (int i=num1.size()-1, j=num2.size()-1; i>=0; i--, j--) {
|
|
x = num1[i]-'0' + carry;
|
|
if(j>=0){
|
|
x += num2[j]-'0';
|
|
}
|
|
s.insert(s.begin(), x%10+'0');
|
|
carry = x/10;
|
|
}
|
|
if (carry>0) {
|
|
s.insert(s.begin(), carry+'0');
|
|
}
|
|
|
|
return s;
|
|
}
|
|
|
|
|
|
string multiply(string num1, string num2) {
|
|
|
|
if (num1.size()<=0 || num2.size()<=0) return "";
|
|
|
|
string result;
|
|
for ( int i=num1.size()-1; i>=0; i--) {
|
|
int carry = 0;
|
|
string val;
|
|
for( int j=num2.size()-1; j>=0; j--) {
|
|
int v = (num2[j]-'0') * (num1[i]-'0') + carry;
|
|
val.insert(val.begin(), v%10+'0');
|
|
carry = v/10;
|
|
}
|
|
if (carry) val.insert(val.begin(), carry+'0');
|
|
for (unsigned int j=i; j<num1.size()-1; j++) {
|
|
val.push_back('0');
|
|
}
|
|
result = strPlus(result, val);
|
|
}
|
|
|
|
//check if it is zero
|
|
if (result[0]=='0') return "0";
|
|
return result;
|
|
|
|
}
|
|
};
|
|
|
|
|
|
|
|
int main(int argc, char**argv)
|
|
{
|
|
string s1="20";
|
|
string s2="25";
|
|
if (argc>2){
|
|
s1 = argv[1];
|
|
s2 = argv[2];
|
|
}
|
|
cout << s1 << " * " << s2 << " = " << multiply(s1, s2) << endl;
|
|
return 0;
|
|
}
|