字符串相乘（算法）

给出两个字符串表示的正整数，求其乘积，返回其乘积的字符串。

public string multiply(String num1,String num2){int len1 = num1.length ,len2 = num2.length ;int [] num = new int[len1 + len2];int n = num.length;for(int i = len1 - 1;i >= 0;i--)for(int j = len2 - 1; j >= 0; j--){num[i + j + 1] += (num1.charAt(i) - '0' ) * (num2.charAt(j) - '0');}int carry = 0;for(int i = n - 1; i >= 0; i--){num[i] += carry;carry = num[i] / 10;num[i] = num[i] % 10;}String result = "";boolean firstNonzero = false;for(int i = 0; i < n; i++){if(!firstNonzero && num[i] == 0)continue;else{result += num[i];firstNonzero = true;}}if( result.equals("")) return "0";return result;}