LeetCode 43. Multiply Strings（乘法）

原题网址：https://leetcode.com/problems/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.

方法：模拟乘法运算。

public class Solution {    public String multiply(String num1, String num2) {        int[] n1 = new int[num1.length()];        int[] n2 = new int[num2.length()];        int[] m = new int[num1.length() + num2.length()];        for(int i=0; i<n1.length; i++) {            n1[n1.length-1-i] = num1.charAt(i)-'0';        }        for(int i=0; i<n2.length; i++) {            n2[n2.length-1-i] = num2.charAt(i)-'0';        }        for(int i=0; i<n1.length; i++) {            int carry = 0;            for(int j=0; j<n2.length; j++) {                int mul = m[i+j] + n1[i]*n2[j] + carry;                m[i+j] = mul % 10;                carry = mul / 10;            }            if (carry > 0) m[i+n2.length] += carry;        }        boolean notZero = false;        StringBuilder sb = new StringBuilder();        for(int i=m.length-1; i>=0; i--) {            if (m[i] > 0) notZero = true;            if (notZero) sb.append(m[i]);        }        if (!notZero) sb.append(0);        return sb.toString();    }}