Strobogrammatic Number II — LeetCode 247 Python Solution

The problem

Given an integer n, return all the strobogrammatic numbers that are of length n. You may return the answer in any order.

Example

Input

n = 2

Output

["11","69","88","96"]

Python solution

class Solution:
    def findStrobogrammatic(self, n: int) -> List[str]:
        def dfs(u):
            if u == 0:
                return ['']
            if u == 1:
                return ['0', '1', '8']
            ans = []
            for v in dfs(u - 2):
                for l, r in ('11', '88', '69', '96'):
                    ans.append(l + v + r)
                if u != n:
                    ans.append('0' + v + '0')
            return ans

        return dfs(n)

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 247. Strobogrammatic Number II is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

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