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Grokking the Coding Interview Patterns in C++

Solution: Find The K-th Lucky Number

Explore the method to find the k-th lucky number by transforming the integer k into a binary-like string and substituting digits to generate lucky numbers formed only by 4s and 7s. Understand how bitwise manipulation simplifies this process, achieving a time complexity of O(log k) and space complexity of O(log k).

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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 ...