金山的笔试题--代码编写部分--大数相加

呃,啥都不说了,哥将近半个月没写代码,先前代码写的也少,一下脑袋就闷了.不过好歹底子还在.总算花了点时间搞出来了.

public class BigNumberAdd {

    /**
     * @param args
     */
    public static void main(String[] args) {
        String add = "9";
        String added = "1";

        System.out.println(bigNumadd(add, added));

    }

    /**
     * 如果出现加数或者被加数为负数,则算法会失效
     * @param add 加数
     * @param added 被加数
     * @return 相加结果
     *
     */
    public static String bigNumadd(String add, String added) {
        int addLen = add.length();
        int addedLen = added.length();
        int carray = 0;
        StringBuffer result = new StringBuffer();
        int i = addLen - 1;
        int j = addedLen - 1;
        int a = 0;
        int b = 0;
        int r = 0;
        for (; i >= 0 && j >= 0; i--, j--) {
            a = Integer.parseInt(add.substring(i, i + 1));
            b = Integer.parseInt(added.substring(j, j + 1));
            r = a + b + carray;
            if (r < 10) {
                carray = 0;
                result.insert(0, r);
            } else {
                carray = 1;
                result.insert(0, r % 10);
            }
        }
        if (addLen > addedLen) {
            for (; i >= 0; i--) {
                a = Integer.parseInt(add.substring(i, i + 1));
                r = a + carray;
                if (r < 10) {
                    carray = 0;
                    result.insert(0, r);
                } else {
                    carray = 1;
                    result.insert(0, r % 10);
                }
            }
            if (carray != 0) {
                result.insert(0, 1);
            }
        } else if (addedLen > addLen) {
            for (; j >= 0; j--) {
                b = Integer.parseInt(added.substring(j, j + 1));
                r = b + carray;
                if (r < 10) {
                    carray = 0;
                    result.insert(0, r);
                } else {
                    carray = 1;
                    result.insert(0, r % 10);
                }
            }
            if (carray != 0) {
                result.insert(0, 1);
            }
        } else {
            if (carray != 0) {
                result.insert(0, 1);
            }
        }
        return result.toString();
    }

}