Rotated Digits — LeetCode 788 Python Solution

The problem

An integer x is a good if after rotating each digit individually by 180 degrees, we get a valid number that is different from x. Each digit must be rotated - we cannot choose to leave it alone.

Example

Input

n = 10

Output

4

Explanation

There are four good numbers in the range [1, 10] : 2, 5, 6, 9.

Python solution

class Solution:
    def rotatedDigits(self, n: int) -> int:
        def check(x):
            y, t = 0, x
            k = 1
            while t:
                v = t % 10
                if d[v] == -1:
                    return False
                y = d[v] * k + y
                k *= 10
                t //= 10
            return x != y

        d = [0, 1, 5, -1, -1, 2, 9, -1, 8, 6]
        return sum(check(i) for i in range(1, n + 1))

Complexity

Pattern: Dynamic Programming

Define a state, write the transition, and stop recomputing the same subproblem. LeetCode 788. Rotated Digits is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Dynamic Programming.

The dynamic programming guide has the Python template for the pattern and the 481 LeetCode problems that use it.

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