Multiply Strings Java

LeetCode

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.

	public class MultiplyStrings {
	public String multiply(String num1, String num2) {
	if (num1==null||num1.length()==0||num2==null||num2.length()==0){
	return null;
	}
	int[] nums=new int[num1.length()+num2.length()];
	for (int i=0; i<num2.length(); i++){
	int carry=0;
	int a=num2.charAt(num2.length()-i-1)-'0';
	for (int j=0; j<num1.length(); j++){
	int b=num1.charAt(num1.length()-1-j)-'0';
	nums[i+j]+=a*b+carry;
	carry=nums[i+j]/10;
	nums[i+j]%=10;
	}
	nums[i+num1.length()]+=carry;
	}
	StringBuffer result=new StringBuffer();
	int i=nums.length-1;
	while(i>0&&nums[i]==0){
	i--;
	}
	while(i>=0){
	result.append(nums[i]);
	i--;
	}
	return result.toString();
	}
	}

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