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stacks_and_queues/README.md

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+### stacks
+
+<br>
+
+* last in, first out structures (LIFO)
+* useful in certain recursive algorithms, where you can push temp data as you recurse, and remove them from the (memory or data structure) stack as you backtrace.
+
+
+<br>
+
+----
+
 ### queues 
 
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-* queues can be implemented with two arrays or a dynamic array (linked list).
-* if implemented with a dynamic array, a more efficient solution is to use a circular queue (ring buffer), i.e. a fixed-size array and two pointers to indicate the starting and ending positions.
-* an advantage of circular queues is that we can use the spaces in front of the queue. in a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. but using the circular queue, we can use the space to store new values.
+* first in, first out structures (FIFO), i.e., items are removed at the same order they are added.
+* queues can be implemented with two arrays or a dynamic array (linked list), as long as items are added and removed from opposite sides.
+* if implemented with a dynamic array, a more efficient solution is to use a circular queue (ring buffer), i.e. a fixed-size array and two pointers to indicate the starting and ending positions. an advantage of circular queues is that we can use the spaces in front of the queue. in a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. but using the circular queue, we can use the space to store new values.
+* queues are often used in breath-first search (where you store a list of nodes to be processed) or when implementing a cache.
 
 
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