Leetcode 2802. Find The K-th Lucky Number

Generate the k-th positive integer whose decimal representation consists only of digits 4 and 7 (the "lucky" numbers), ordered by value. The challenge is to handle large k efficiently by recognizing the bijection between binary patterns (or lengths and combinations) and lucky-number strings rather than brute-force enumeration.

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Leetcode 2802. Find The K-th Lucky Number

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