66. Plus One

66. Plus One

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

The digits are stored such that the most significant digit is at the head of the list, and each element in the array contain a single digit.

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

Example 1:

Input: [1,2,3]
Output: [1,2,4]
Explanation: The array represents the integer 123.

Example 2:

Input: [4,3,2,1]
Output: [4,3,2,2]
Explanation: The array represents the integer 4321.

My Solutions:

从array 末尾开始，用for loop加上1，如果加上1的结果小于等于9，直接return。不然说明要进位，把当前位记作0。

如果for loop结束后还没有return过，说明之前的数为999....，直接新建一个更大的数组，第一个数字为1，其余数字默认为0，返回此数组。

Time: O(n)

public class Solution {
    public int[] plusOne(int[] digits) {
        for (int i = digits.length - 1; i >= 0; i--) {
            digits[i] += 1;
            if (digits[i] <= 9) return digits;
            digits[i] = 0;
        }
        int[] res = new int[digits.length + 1];
        res[0] = 1;
        return res;
    }
}