(Java)LeetCode-43. 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.
• Converting the input string to integer is NOT allowed.

• You should NOT use internal library such as BigInteger.

这道题蛮简单的，算两个大数的乘法，模拟手算时的竖式计算即可，需要做MN次乘法和若干次加法，需要耐心~代码如下：

public class Solution {    public String multiply(String num1, String num2) {int len1 = num1.length();int len2 = num2.length();if(num1.equals("0")|| num2.equals("0"))    return "0";int len = len1 + len2-1;int carry = 0;int temp = 0, templeft = 0, tempright = 0;int sum = 0;Stack<Integer> st = new Stack<Integer>();for(int i = 1; i <= len; i++){for(int j = 1; j <= i; j++){if( i+1-j > len2 || j > len1){continue;}templeft = Integer.parseInt(num1.substring(len1-j, len1-j+1)); tempright = Integer.parseInt(num2.substring(len2-1-i+j, len2-i+j));temp = templeft * tempright;sum = temp + sum;}sum +=carry;st.push(sum % 10);carry = sum/10;sum = 0;}while(carry != 0){st.push(carry % 10);carry /= 10;}StringBuilder sb = new StringBuilder();while(!st.isEmpty()){sb.append(st.pop());}return sb.toString();    } }