leetcode43-字符串相乘

字符串相乘

• 逐位相乘

class Solution {
    public String multiply(String num1, String num2) {
        if(num1.equals("0") || num2.equals("0"))    return "0";
        int m = num1.length(), n = num2.length();
        int arr[] = new int[m+n];
        for(int i = m-1; i >= 0; i--){
            int x = num1.charAt(i)-'0';
            for(int j = n-1; j >= 0; j--){
                int y = num2.charAt(j)-'0';
                arr[i+j+1] += x*y;
            }
        }
        for(int i = m+n-1; i > 0; i--){
            arr[i-1] += arr[i] / 10;
            arr[i] %= 10;
        }
        int index = arr[0] == 0 ? 1 : 0;
        StringBuilder sb = new StringBuilder();
        while(index < m+n){
            sb.append(arr[index]);
            index++;
        }
        return sb.toString();
    }
}