[Swift]LeetCode967. 连续差相同的数字 | Numbers With Same Consecutive Differences

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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 except for the number 0 itself. For example, 01 has one leading zero and is invalid, but 0 is valid.

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]

Note:

1. 1 <= N <= 9
2. 0 <= K <= 9

---

返回所有长度为 N 且满足其每两个连续位上的数字之间的差的绝对值为 K 的非负整数。

请注意，除了数字 0 本身之外，答案中的每个数字都不能有前导零。例如，01 因为有一个前导零，所以是无效的；但 0 是有效的。

你可以按任何顺序返回答案。

示例 1：

输入：N = 3, K = 7
输出：[181,292,707,818,929]
解释：注意，070 不是一个有效的数字，因为它有前导零。

示例 2：

输入：N = 2, K = 1
输出：[10,12,21,23,32,34,43,45,54,56,65,67,76,78,87,89,98]

提示：

1. 1 <= N <= 9
2. 0 <= K <= 9

---

16ms

class Solution {
    
    func numsSameConsecDiff(_ digitCount: Int, _ difference: Int) -> [Int] {
        var result = [Int]()

        let start = (digitCount == 1) ? 0 : 1
        let end = 9

        for i in start...end {
            let tempResult = Result()
            numsSameConsecDiff(digitCount-1, difference, i, tempResult)
            if !tempResult.val.isEmpty {
                result.append(contentsOf: tempResult.val)
            }
        }
        
        return result
    }

    class Result {
        var val: [Int] = []
    }

    func numsSameConsecDiff(_ digitCount: Int, _ difference: Int, _ number: Int, _ result: Result) {
        guard digitCount > 0 else {
            result.val.append(number)
            return
        }

        let makeNumber: (Int) -> Void = { (nextDigit) in
            if nextDigit >= 0 && nextDigit <= 9 {
                self.numsSameConsecDiff(digitCount - 1, difference, number * 10 + nextDigit, result)
            }
        }

        let lastDigit = number % 10

        makeNumber(lastDigit + difference)

        if difference != 0 {
            makeNumber(lastDigit - difference)
        }
    }
    
}

---

20ms

class Solution {
    func numsSameConsecDiff(_ N: Int, _ K: Int) -> [Int] {
        var nums: Set = [1, 2, 3, 4, 5, 6, 7, 8, 9]
        
        guard N != 0 else {
            return Array(nums.sorted())
        }
        
        guard N != 1 else {
            nums.insert(0)
            return Array(nums.sorted())
        }
        
        for i in 1...(N - 1) {
            var updatedNums: Set<Int> = []
            for x in nums {
                let lastNumber = x % 10
                if lastNumber + K <= 9 {
                    updatedNums.insert(10*x + (lastNumber + K))
                }
                
                if lastNumber - K >= 0 {
                    updatedNums.insert(10*x + (lastNumber - K))
                }
            }
            nums = updatedNums
        }
        
        if N == 0 {
            nums.insert(0)
        }
        
        return Array(nums.sorted())
        
    }
}

---

24ms

class Solution {
    func numsSameConsecDiff(_ N: Int, _ K: Int) -> [Int] {
        var res = [Int]()
        if N == 1 {
            return [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
        }
        for i in 1...9 {
            res += helper(N - 1, K, i, i)
        }
        return res
    }
    
    func helper(_ N: Int, _ K: Int, _ num: Int, _ digit: Int) -> [Int] {
        if digit > 10 || digit < 0 { return [] }
        if N == 0 {
            return []
        }
        var res = [Int]()
        if digit + K < 10 {
            res.append(num * 10 + digit + K)
        }
        if K != 0 {
            if digit - K >= 0 {
            res.append(num * 10 + digit - K)
        }
        }
        
        if N == 1 {
            return res
        }
        
        var ret = [Int]()
        for r in res {
            let a = helper(N - 1, K, r, r % 10)
            for aa in a {
                ret.append(aa)
            }
        }
        return ret
    }
}

---

28ms

class Solution {
    var v:[Int] = [Int]()
    var n:Int = 0
    var k:Int = 0
    var val:Int = 0
    func numsSameConsecDiff(_ N: Int, _ K: Int) -> [Int] {
        if N == 1
        {
            for i in 0...9
            {
                v.append(i)
            }
            return v
        }
        n = N
        k = K
        val = 0
        dfs(0,0)
        v = v.sorted(by:>)
        return v
    }
    
    func dfs(_ cur:Int,_ pr:Int)
    {
        if cur == n
        {
            v.append(val)
            return
        }
        for i in 0...9
        {
            if cur == 0
            {
                if i != 0
                {
                    val = i
                    dfs(cur + 1,i)
                }
            }
            else
            {
                val *= 10 
                val += i
                if abs(pr - i) == k
                {
                    dfs(cur + 1, i)
                }
                val -= i
                val /= 10
            }
        }
    }
}