题解 | #大数加法#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     * 计算两个数之和
     * @param s string字符串 表示第一个整数
     * @param t string字符串 表示第二个整数
     * @return string字符串
     */
    public String solve (String s, String t) {
        // write code here
        if (s == null || t == null) {
            return s != null ? s : t;
        }
        char[] sArr = s.toCharArray();
        char[] tArr = t.toCharArray();
        int sLen = sArr.length;
        int tLen = tArr.length;
        int maxLen = Math.max(sLen, tLen);
        int i = sLen - 1;
        int j = tLen - 1;
        int cur = 0;
        int pre = 0;
        List<Integer> list = new LinkedList<>();
        for (int k = 0; k < maxLen; k++) {
            int first = i >= 0 ? (int) (sArr[i] - '0') : 0;
            int second = j >= 0 ? (int) (tArr[j] - '0') : 0;
            int sum = first + second + pre;
            cur = sum % 10;
            pre = sum / 10;
            list.add(cur);
            i--;
            j--;
        }
        if (pre > 0) {
            list.add(pre);
        }
        StringBuilder sb = new StringBuilder();
        Collections.reverse(list);
        for (int num : list) {
            sb.append(num);
        }
        return sb.toString();
    }
}