Eric Walker added Advent of Code to Algorithm coding challenges

Eric Walker added a number of topics and a number of links to Algorithms and data structures, and added Algorithms and data structures to Software and programming

Eric Walker added 673. Number of Longest Increasing Subsequence and 152. Maximum Product Subarray to Coding challenges involving array subsequences, and added Coding challenges involving array subsequences to Algorithm coding challenges

Eric Walker added 673. Number of Longest Increasing Subsequence and 523. Continuous Subarray Sum to Coding challenges involving dynamic programming (DP), and added Coding challenges involving dynamic programming (DP) to Algorithm coding challenges

Eric Walker added 18. 4Sum and 454. 4Sum II to 4Sum, and added 4Sum to Algorithm coding challenges

Eric Walker added 15. 3Sum to 3Sum, and added 3Sum to Algorithm coding challenges

Eric Walker added a number of topics to Algorithm coding challenges, and added Algorithm coding challenges to Algorithms and data structures