LeetCode 1056. Confusing Number

Description

https://leetcode.com/problems/confusing-number/

Given a number N, return true if and only if it is a confusing number, which satisfies the following condition:

We can rotate digits by 180 degrees to form new digits. When 0, 1, 6, 8, 9 are rotated 180 degrees, they become 0, 1, 9, 8, 6 respectively. When 2, 3, 4, 5 and 7 are rotated 180 degrees, they become invalid. A confusing number is a number that when rotated 180 degrees becomes a different number with each digit valid.

Example 1:

Input: 6
Output: true
Explanation: 
We get 9 after rotating 6, 9 is a valid number and 9!=6.

Example 2:

Input: 89
Output: true
Explanation: 
We get 68 after rotating 89, 86 is a valid number and 86!=89.

Example 3:

Input: 11
Output: false
Explanation: 
We get 11 after rotating 11, 11 is a valid number but the value remains the same, thus 11 is not a confusing number.

Example 4:

Input: 25
Output: false
Explanation: 
We get an invalid number after rotating 25.

Note:

  1. 0 <= N <= 10^9
  2. After the rotation we can ignore leading zeros, for example if after rotation we have 0008 then this number is considered as just 8.

Explanation

Create a mapping between numbers and their rotated numbers and check if the reversed string can be same as their rotated string.

Python Solution

class Solution:
    def confusingNumber(self, N: int) -> bool:
        mapping = {
            '0': '0',
            '1': '1',            
            '6': '9',
            '8': '8',
            '9': '6',            
        }
        
        rotated_str = ""
        n_str = str(N)
        for c in n_str[::-1]:
            if c not in mapping:
                return False
            else:
                rotated_str += mapping[c]
                
        return rotated_str != n_str
                
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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