[leetcode] Plus One

Given a non-negative number represented as an array of digits, plus one to the number.

The digits are stored such that the most significant digit is at the head of the list.

例如：98，存储为：array[0]=9; array[1]=8。

思路：从数组的最后一位开始加1，需要考虑进位，如果到[0]位之后仍然有进位存在，需要新开一个长度为 digits.length + 1 的数组，拷贝原数组到该数组中。

JAVA代码：

public int[] plusOne(int[] digits) {
        if (digits == null || digits.length == 0) {
            return null;
        }
        int top = 0;
        int flag = 1;
        int i = digits.length - 1;
        int[] tmp = null;
        while (i >= 0) {
            if (top > 0) {
                int sum = digits[i] + top;
                if (sum >= 10) {
                    top = 1;
                    digits[i] = sum - 10;
                }
                else {
                    digits[i] = sum;
                    top = 0;
                }
            }
            if (flag == 1) {
                int sum = digits[i] + 1;
                if (sum >= 10) {
                    top = 1;
                    digits[i] = sum - 10;
                }
                else {
                    digits[i] = sum;
                }
                flag = 0;
            }
            if (top == 0) {
                break;
            }
            else {
                i --;
            }
        }
        if (top > 0) {
            tmp = new int[digits.length + 1];
            tmp[0] = top;
            for (int j = 1; j < tmp.length; j++) {
                tmp[j] = digits[j - 1];
            }
        }
        return tmp == null ? digits : tmp;
    }