leetcode 43. 字符串相乘(java)

java:

先不处理进位，最后单独处理

class Solution {
    public String multiply(String num1, String num2) {
        if(num1.equals("0") || num2.equals("0")) return "0";
        char[] n1 = num1.toCharArray();
        char[] n2 = num2.toCharArray();
        int[] ans = new int[n1.length + n2.length];

        for(int i = 0; i < n1.length; i ++){
            for(int j = 0; j < n2.length; j ++){
                ans[i + j + 1] += (n1[i] - '0') * (n2[j] - '0');
            }
        }

        for(int k = ans.length - 1; k >= 0; k --){
            if(ans[k] >= 10){
                ans[k - 1] += ans[k] / 10;
                ans[k] %= 10;
            }
        }
        StringBuilder sb = new StringBuilder();
        for(int i : ans) sb.append(i);
        if (sb.charAt(0) == '0') sb.deleteCharAt(0);
        return sb.toString();
    }
}