Add Interactive data structures algorithms reference (#10844)

* Update free-programming-books-langs.md

* Update free-programming-books-langs.md

Adjust Spacing between headers and sections

* Update free-programming-playgrounds.md with Gremlin

Add Gremlin Playground reference

* Update free-programming-playgrounds.md

* Add gremlin cheatsheets and samples

* New Interactive Algorithms data structure

* Reset branch to main state for other pr file.

* Fix blank line linter error

more/free-programming-interactive-tutorials-en.md

@@ -1,6 +1,7 @@
 ### Index
 
 * [Ada](#ada)
+* [Algorithms](#algorithms)
 * [Android](#android)
 * [Bash](#bash)
 * [C](#c)
@@ -58,6 +59,11 @@
 * [Introduction to Ada](https://learn.adacore.com/courses/intro-to-ada/index.html) - Adacore
 
 
+### Algorithms
+
+* [Data Structures Visualization](https://www.cs.usfca.edu/~galles/visualization/Algorithms.html) - David Galles
+
+
 ### Android
 
 * [Android Tutorial](https://www.tutlane.com/tutorial/android) - tutlane