algorithms
==========
btree
datastructure:
	datastructure.c: simple stack; simple queue; sentinel linked list with
	a free head to book unused node(implemented by array); chained 
	multiplicaton hash table; double hashing open addressing hash table
dynamic_programming:
	assembly_line.c
	longest_comm_subseq.c
	matrix_chain.c
	optimal_tree.c
greedy_algorithm:
	activity_selection.c
	huffman_code.c
priority_queue
	priority_queue.c
selection:
	selection.c: select min and max which saves 1/4 time from normal;
	select ith least with random partitioning; select ith least with 
	median of medians partitioning selection in worst case linear time
sort:
	sort.c: insertion sort; merge sort; permute array by sorting; 
	permute array by random in place; heap sort; quick sort; randomized
	quick sort; counting sort; radix sort; bucket sort
tree:
	interval_tree.c
	ostree.c: order statistic tree
	tree.c: binary search tree; red black tree