066.Plus One

Posted on | In

Solution 1: accepted 6%

Brute force with low efficiency.
Q: How to add a new digit at the beginning of an array efficiently? 

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
public class Solution {
    public int[] plusOne(int[] digits) {
        
        int len = digits.length;
        int tail = len - 1;
        
        // Increment the last digit
        digits[tail]++;
        
        // Check whether digits are carried over
        while (digits[tail] > 9 && tail > 0) {
            digits[tail] = 0;
            digits[tail - 1]++;
            tail -= 1;
        }
        
        // If the first number is incremented and cause a new digit at the beginning
        if (digits[0] > 9) {
            digits[0] = 0;
            int[] update = new int[len + 1];
            update[0] = 1;
            for (int i = 1; i < len + 1; i++) {
                update[i] = digits[i - 1];
            }
            return update;
        }
        
        return digits;
        
        
        
    }    
}

Solution 2: accepted

No array manipulation. 

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
public class Solution {
    public int[] plusOne(int[] digits) {
        
        int len = digits.length;
        
        // If the current digit does not cause a carry, return the updated array immediately
        for (int i = len - 1; i >= 0; i--) {
          if (digits[i] < 9) {
              digits[i]++;
              return digits;
          }
          digits[i] = 0;
        }
        
        // If the entire array is consisted of "9"s, return a new array leading with a "1" followed by "0"s
        int[] update = new int[len + 1];
        update[0] = 1;
        return update;        
    }    
}