[LeetCode]43. Multiply Strings

https://leetcode.com/problems/multiply-strings/?tab=Description

大整数乘法

结果当前位的值不是马上能算出来的！

双层循环，内层每循环一次得到外层当前位乘内层数的乘积。外层再前移一位，接着算。

这个题要好好看下

public class Solution { public String multiply(String num1, String num2) { int[] res = new int[num1.length() + num2.length()]; for (int i = num1.length() - 1; i >= 0; i--) { for (int j = num2.length() - 1; j >= 0; j--) { int multi = (num1.charAt(i) - '0') * (num2.charAt(j) - '0'); int p1 = i + j; int p2 = i + j + 1; int sum = multi + res[p2]; res[p1] += sum / 10; res[p2] = sum % 10; } } StringBuilder sb = new StringBuilder(); for (int r : res) { if (!(sb.length() == 0 && r == 0)) { sb.append(r); } } return sb.length() == 0 ? "0" : sb.toString(); } }