Super Lucky Palindromes
Time limit1sMemory limit1024 MB
Given k, find the k-th smallest palindrome whose digits are all 4 or 7, whose digit count is lucky, and whose count of 4s or 7s is lucky.
- Level
Medium6 of 10
- Topics
- Combinatorics, Math, Implementation
- Solved
- No attempts yet
Problem
Lucky numbers are positive integers made only of the digits 4 and 7. For example, 47477 and 777 are lucky numbers, while 457 and 1232 are not.
A super lucky number satisfies all of the following conditions.
- It is a lucky number.
- Its number of digits is a lucky number.
- The count of 4s or the count of 7s in it is a lucky number (both counts may be lucky numbers).
A palindrome is an integer that reads the same forwards and backwards. For example, 547745 and 343 are palindromes, while 74 and 12345 are not. A super lucky palindrome is a positive integer that is both a super lucky number and a palindrome.
Given k, print the k-th smallest super lucky palindrome.
Input
The first line contains a positive integer n, the number of queries. Each of the next n lines contains a single integer k ().
Output
For each query, print 'Query #d: ' followed by the k-th smallest super lucky palindrome, where d is the query number starting from 1.