Leetcode - 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.

Solution:

Solution 1: recursion

class Solution {
    public int[] plusOne(int[] digits) {
      int units = digits[digits.length-1]+1;
      if(units < 10){
         digits[digits.length-1] = units;
         return digits;
      }else{  
         digits[digits.length-1] = units-10;
          // The previous digit plus one
         if(digits.length ==1){
             int[] results = new int[digits.length+1];
             results[0] =1;
             results[1] = digits[0];
             return results; 
         }else{
             int[] pre = new  int[digits.length-1];
             for(int i=0;i<pre.length;i++){
                 pre[i] = digits[i];
             }
            int[] next= plusOne(pre);
            int[] results = new int[next.length+1];
            for(int i=0;i<results.length;i++){
                if(i!=results.length-1){
                    results[i] = next[i];
                }else{
                    results[i] = digits[digits.length-1];
                }
            }
            return results;
         }
      }
    }
}

Solution 2: Offcial solution

class Solution {
    public int[] plusOne(int[] digits) {
        for (int i = digits.length - 1; i >= 0; i--) {
            digits[i]++;
            digits[i] = digits[i] % 10;
            if (digits[i] != 0) return digits;
        }
        digits = new int[digits.length + 1];
        digits[0] = 1;
        return digits;
    }
}

Conclusion:

递归移位+1