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.

解析

很簡單，就是把一個數組當成數字加一，考慮下進位就行了。

參考答案（自己寫的）：

class Solution {
    public int[] plusOne(int[] digits) {
        int index = digits.length-1;
        if (digits[index] != 9) {
            digits[index] += 1;
            return digits;
        }
        digits[index] = 0;
        index--;
        while(index >= 0 && digits[index] == 9) {
            digits[index--] = 0;
        }
        if (index < 0) {
            int[] res = new int[digits.length + 1];
            res[0] = 1;
            return res;
        } else {
            digits[index] += 1;
            return digits;
        }
    }
}
 

當需要增加一位的時候需要new一個數組出來，把0位置上的數字置一就行了，其他位置默認就是0；

[leetcode][66] Plus One