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Multiply Strings

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 Solution {  public static String multiply(String num1, String num2) {      if(num1.equals("0") || num2.equals("0"))			return "0";		if (hasSign(num1))			num1 = num1.substring(1);		if (hasSign(num2))			num2 = num2.substring(1);		StringBuilder sb = new StringBuilder();		int len_1 = num1.length();		int len_2 = num2.length();		int flag_mul =0;		int tmp_1=0;		if (len_1 <= len_2) {			if (len_1 == 1) {				int tmp = Integer.parseInt(num1);				for (int i = 0; i < len_2; i++) {					tmp_1 = Integer.parseInt(num2.substring(len_2-1-i,len_2-i));					tmp_1 = tmp* tmp_1;					tmp_1 +=flag_mul;					flag_mul = tmp_1 /10;					tmp_1 = tmp_1%10;					sb.append(tmp_1);				}				if(flag_mul != 0 )					sb.append(flag_mul);				sb.reverse();			}else{				sb.append(0);				for(int i=0;i
    
     0;j--){						sb.append(0);					}					String str_tmp_2 = StrAdd(str_tmp, sb.toString());					sb.setLength(0);					sb.append(str_tmp_2);				}			}		} else {			if (len_2 == 1) {				int tmp = Integer.parseInt(num2);				for (int i = 0; i < len_1; i++) {					tmp_1 = Integer.parseInt(num1.substring(len_1-1-i,len_1-i));					tmp_1 = tmp* tmp_1;					tmp_1 +=flag_mul;					flag_mul = tmp_1 /10;					tmp_1 = tmp_1%10;					sb.append(tmp_1);				}				if(flag_mul != 0 )					sb.append(flag_mul);				sb.reverse();			}else{				sb.append(0);				for(int i=0;i
     
      0;j--){						sb.append(0);					}					String str_tmp_2 = StrAdd(str_tmp, sb.toString());					sb.setLength(0);					sb.append(str_tmp_2);				}			}		}		return sb.toString();	}	public static String StrAdd(String num1, String num2) {		StringBuilder sb = new StringBuilder();		if (hasSign(num1))			num1 = num1.substring(1);		if (hasSign(num2))			num2 = num2.substring(1);		sb.setLength(0);		int len_1 = num1.length();		int len_2 = num2.length();		boolean flag_add = false;		int tmp = 0;		if (len_1 <= len_2) {			for (int i = 0; i < len_1; i++) {				tmp = Integer						.parseInt(num1.substring(len_1 - 1 - i, len_1 - i))						+ Integer.parseInt(num2.substring(len_2 - 1 - i, len_2								- i));				if (flag_add == true) {					tmp++;					flag_add = false;				}				if (tmp >= 10) {					tmp -= 10;					flag_add = true;				}				sb.append(tmp);			}			for (int i = len_1; i < len_2; i++) {				tmp = Integer						.parseInt(num2.substring(len_2 - 1 - i, len_2 - i));				if (flag_add == true) {					tmp++;					flag_add = false;				}				if (tmp >= 10) {					tmp -= 10;					flag_add = true;				}				sb.append(tmp);			}			if (flag_add == true) {				flag_add = false;				sb.append(1);			}		} else {			for (int i = 0; i < len_2; i++) {				tmp = Integer						.parseInt(num1.substring(len_1 - 1 - i, len_1 - i))						+ Integer.parseInt(num2.substring(len_2 - 1 - i, len_2								- i));				if (flag_add == true) {					tmp++;					flag_add = false;				}				if (tmp >= 10) {					tmp -= 10;					flag_add = true;				}				sb.append(tmp);			}			for (int i = len_2; i < len_1; i++) {				tmp = Integer						.parseInt(num1.substring(len_1 - 1 - i, len_1 - i));				if (flag_add == true) {					tmp++;					flag_add = false;				}				if (tmp >= 10) {					tmp -= 10;					flag_add = true;				}				sb.append(tmp);			}			if (flag_add == true) {				flag_add = false;				sb.append(1);			}		}		return sb.reverse().toString();	}	public static boolean hasSign(String num) {		if (num.charAt(0) == '-' || num.charAt(0) == '+')			return true;		else			return false;	}}
     
    

 

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