算法题实现并返回，2个长整数的字符串相加的和，比如”1234567890” + “99” = “1234567989”，不能直接转成bigdeciaml 或 long相加

    1. public class Main {
    3.     public static void main(String[] args) {
    4.         System.out.println(sumStr("507", "593"));
    5.     }
    7.     public static String sumStr(String m, String n) {
    9.         char[] ms = m.toCharArray();
    10.         char[] ns = n.toCharArray();
    12.         if (ms.length > ns.length) {
    13.             return String.valueOf(sum(ms, ns));
    14.         } else {
    15.             return String.valueOf(sum(ns, ms));
    16.         }
    17.     }
    19.     /**
    20.      *
    21.      * @param ms 长数组
    22.      * @param ns 短数组
    23.      * @return
    24.      */
    25.     public static char[] sum (char[] ms , char[] ns) {
    26.         boolean flag = false;
    27.         for (int i = ms.length-1; i > -1; i--) {
    28.             // 短数组下表
    29.             int index = ns.length - (ms.length - i);
    30.             // 下标边界
    31.             if (index > -1) {
    32.                 int sum = Integer.valueOf(ms[i] + "") + Integer.valueOf(ns[index] + "");
    33.                 sum = flag ? sum + 1 : sum;
    34.                 int mod = sum % 10;
    35.                 flag = sum > 9;
    36.                 ms[i] = ((flag ? mod : sum) + "").toCharArray()[0];
    37.             } else if (!flag){
    38.                 break;
    39.             } else {
    40.                 int sum = Integer.valueOf(ms[i] + "") + 1;
    41.                 int mod = sum % 10;
    42.                 flag = sum > 9;
    43.                 ms[i] = ((flag ? mod : sum) + "").toCharArray()[0];
    44.             }
    45.         }
    46.         // 结果位数是否超过最长数组
    47.         if (flag) {
    48.             char[] msplus = new char[ms.length+1];
    49.             msplus[0] = '1';
    50.             for (int i = 0; i < ms.length; i++) {
    51.                 msplus[i+1] = ms[i];
    52.             }
    53.             return msplus;
    54.         } else {
    55.             return ms;
    56.         }
    57.     }
    58. }