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Solution: Find The K-th Lucky Number

Explore how to find the k-th lucky number consisting of digits 4 and 7 by converting k into a binary-like format. Understand the step-by-step process of transforming the binary digits into a lucky number string using bitwise manipulation, optimizing both time and space complexity for effective problem-solving.

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Statement

A number is called lucky if it comprises only the digits 44 and 77. Your task is to return the k-th lucky number as a string for a given integer k. 

Constraints:

  • 1<=1 <= k <=109<= 10^9

Solution

The essence of this solution lies in using bitwise manipulation to generate the k-th lucky number. The solution uses an approach by transforming the given integer k into a binary-like representation to determine the k-th lucky number. The key idea is to convert k into a string of digits composed of 4s4s ...