66. Plus One

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

You may assume the integer do not contain any leading zero, except the number 0 itself.

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

这道题的要求是给定一个数组表示非负整数，其高位在数组的前面，对这个整数加1。

思路：和加法一样，从后往前遍历，若该位元素<9,则加一，若该位元素为9，则加一后该位元素为0。若数组中元素全是9，则结果比原数组长度大一，第一个元素为1，其余均为0。

    public int[] plusOne(int[] digits) {
        int carry  =1;
        for (int i=digits.length-1;i>=0;i--)
        {
            int sum = carry + digits[i];
            digits[i] = sum%10;
            carry = sum/10;
        }
        if (carry ==0) return digits;
        int[] result = new int[digits.length+1];
        result[0] = carry;
        for (int i=0;i<digits.length;i++)
        {
            result[i+1] = digits[i];
        }
        return result;        
    }