follow_search.py

#!/usr/bin/env python

# Question:
# 	If user_1 followed user_2, we will get an array item like:
#   	[id_1, id_2]
# 	Here is a sample user relationship list:
# 		[ [2, 3], [1, 4], [3, 2], [1, 3], [4, 2], [7, 2], [5, 3], [4, 1] ]
# 	If two items have two same IDs, print one of the them out.
# 	So if we print out [3, 2] and [1, 4], that should be a right result.

rel_list = [ [2, 3], [1, 4], [3, 2], [1, 3], [4, 2], [7, 2], [5, 3], [4, 1] ]
digit_weight = 10 ** len(
	str(
		max(
			[item for sublist in rel_list for item in sublist]
		)
	)
)

# Get the weight value of the relationship.
def weight (rel):
	a, b = rel if rel[0] < rel[1] else rel[::-1]
	return a * digit_weight + b

# Simulate to trigger the comparison event.
def compare_event (e):
	if e['val'] == 0:
		print e['rel']

def compare (a, b):
	val = weight(a) - weight(b)
	compare_event({ 'val': val, 'rel': a })
	return val

# The default sort algorithm in Ruby is Quick Sort, which is plenty good here.
#   Time: average O(log n) | worst n * n
# Memory: average log n    | worst n
sorted(rel_list, compare)