967. Numbers With Same Consecutive Differences (M)

Return all non-negative integers of length n such that the absolute difference between every two consecutive digits is k.

Note that every number in the answer must not have leading zeros. For example, 01 has one leading zero and is invalid.

You may return the answer in any order.

Example 1:

Input: n = 3, k = 7
Output: [181,292,707,818,929]
Explanation: Note that 070 is not a valid number, because it has leading zeroes.

Example 2:

Input: n = 2, k = 1
Output: [10,12,21,23,32,34,43,45,54,56,65,67,76,78,87,89,98]

Constraints:

• 2 <= n <= 9

• 0 <= k <= 9

Solution:

Version 1: DFS

Version 2: BFS

先定下第一位的数字1-9， 再依次BFS 入栈

i.e，(3,4) --> 1, 14, 141, 147, 1414, 1474

class Solution {
    
    private Queue<Integer> queue; 
    private Set<Integer> resultSet; 
    public int[] numsSameConsecDiff(int n, int k) {
        
        if(n <=0) return new int[]{};
        queue = new LinkedList<Integer>();
        resultSet = new HashSet<Integer>();
        
        for(int i = 1; i<= 9; i++)
        {
            bfs(i, n, k);
        }
        
        return resultSet.stream().mapToInt(Integer::intValue).toArray();
    }
    
    public void bfs(int firstDigit, int n, int k)
    {
        queue.offer(firstDigit);
        int step = 1;
        while(!queue.isEmpty() && step <=n )
        {
            int size = queue.size();
            for(int i = 0;i< size; i++)
            {
                Integer current = queue.poll();
                /*if(Math.log10(current.intValue())+1 == n)
                {
                    resultSet.add(current);
                }*/
                if(String.valueOf(current).length() == n)
                {
                    resultSet.add(current);
                    continue;
                }
                if(current%10 + k <= 9)
                {
                    queue.offer(current*10+current%10+k);
                }
                if(current%10 - k >= 0)
                {
                    queue.offer(current*10+current%10-k);
                }
            }
            step++;
        }
    }  
}