LeetCode_OJ【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.

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由于两个数字可能特别大，因此直接转换为int相乘是错误的。
首先将两个String转换为int数组，然后一位一位模拟乘法就可以了。
下面是本题的JAVA实现。

public class Solution {    public String multiply(String num1, String num2) {        int[] s1 = new int[num1.length()];        int[] s2 = new int[num2.length()];        int[] res = new int[num1.length() + num2.length()];        for(int i = 0 ; i < num1.length() ;i++){        s1[i] = num1.charAt(num1.length() -1 -i) - '0';        }        for(int i = 0 ; i < num2.length() ;i++){        s2[i] = num2.charAt(num2.length() -1 -i) - '0';        }        int middle = 0 ;        for(int i = 0 ; i < num1.length() + num2.length() ; i ++){        for(int j = 0 ; j <= i ; j++){        if(j < num1.length() && i-j < num2.length()){        middle += s1[j]*s2[i-j] ;        }        }        res[i] = middle % 10;        middle = middle / 10;        }        String str = "";        for(int i = 0,flag = 1 ; i < res.length ; i ++){        if(flag == 1 && res[res.length-1 -i] == 0)        continue;        else{        flag = 0;        str += res[res.length-1 -i];        }        }        return str.equals("") ? "0" : str;    }}