Python | Join cycle in list

Sometimes, while dealing with graph problems in competitive programming, we have a list of pairs and we need to find if there is a possible cycle in it, and print all the elements in that cycle. Let’s discuss certain way in which this problem can be tackled.

Method : Using yield + loop + generator
The brute method to perform is to use a generator and keep printing the value if we know that the elements surely form a cycle and this is done by infinite loop and stopping when no more matches are found.

# Python3 code to demonstrate working of 
# Join cycle in list 
# Using yield + loop + generator 
  
# helper function to perform this task  
def cycle(test_list, val, stop = None): 
    temp = dict(test_list) 
    stop = stop if stop is not None else val 
    while True: 
        yield (val) 
        val = temp.get(val, stop) 
        if val == stop: break
  
# initializing list 
test_list = [[6, 7], [9, 6], [7, 9]] 
  
# printing original list 
print("The original list is : " + str(test_list)) 
  
# Join cycle in list 
# Using yield + loop + generator 
# printing result 
print("The cycle elements are : ") 
for ele in cycle(test_list, 6): 
    print(ele) 

Output :

The original list is : [[6, 7], [9, 6], [7, 9]]
The cycle elements are : 
6
7
9

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