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MultiplyStrings.java

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/*

Author: King, wangjingui@outlook.com

Date: Dec 20, 2014

Problem: Multiply Strings

Difficulty: Easy

Source: https://oj.leetcode.com/problems/multiply-strings/

Notes:

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.

Solution: Just like what we do when multiplying integers.

*/

public class Solution {

public String multiply(String num1, String num2) {

int l1 = num1.length(), l2 = num2.length();

if (l1 == 0 || l2 == 0) return new String("");

if (num1.charAt(0) == '0' || num2.charAt(0) == '0') return new String("0");

StringBuffer sb = new StringBuffer();

int[] res = new int[l1+l2];

for (int i = 0; i < l1; ++i) {

for (int j = 0; j < l2; ++j) {

res[i+j+1] += (num1.charAt(i)-'0') *(num2.charAt(j)-'0');

}

}

int c = 0;

for (int i = res.length - 1; i>=1; --i) {

res[i] += c;

c = res[i] / 10;

res[i] = res[i] % 10;

sb.insert(0,res[i]);

}

if (c !=0 || res[0] != 0) {

sb.insert(0,c+res[0]);

}

return sb.toString();

}

}