[leetcode]Multiply Strings

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public class Solution { public String multiply(String num1, String num2) { if (num1.equals("0") || num2.equals("0")) return "0"; String result = "0"; for (int i = num1.length()-1, tailZero = 0; i >= 0; i--, tailZero++){ int current = num1.charAt(i)-'0'; int carry = 0; String temp = ""; for (int j = num2.length()-1; j >= 0; j--){ int v2 = num2.charAt(j)-'0'; int digit = (v2*current+carry)%10; carry = (v2*current+carry)/10; temp = digit+temp; } if (carry != 0) temp = carry+temp; temp = temp + getZeros(tailZero); result = add(result, temp); } return result; } private String getZeros(int n){ String result = ""; for (int i = 0; i < n; i++){ result += "0"; } return result; } private String add(String num1, String num2){ int i = num1.length()-1; int j = num2.length()-1; int carry = 0; String result = ""; while (i >= 0 || j >= 0){ int v1 = i >= 0?num1.charAt(i--)-'0':0; int v2 = j >= 0?num2.charAt(j--)-'0':0; int digit = (v1+v2+carry)%10; carry = (v1+v2+carry)/10; result = digit+result; } if (carry == 1) result = "1"+result; return result; } }