DS points for reference:-

1. Use cases of AVL & RB tree.
   http://stackoverflow.com/questions/5288320/why-is-stdmap-implemented-as-a-red-black-tree
2. Comparision b/w Insertion and Selection Sort & other sorting algo
   https://www.quora.com/When-should-one-use-Insertion-vs-Selection-sort
   https://www.quora.com/What-are-some-real-life-uses-of-merge-sort-insertion-sort-quick-sort-and-heap-sort-algorithms
3. How Merge sorting is used in external sorting using 2 or multiple passes.
   https://en.wikipedia.org/wiki/External_sorting
4. Why we need stable sorting?
   http://stackoverflow.com/questions/808617/what-is-the-benefit-for-a-sort-algorithm-to-be-stable
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