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Python | Check the order of characters in a string using OrderedDict ()

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Examples:

  Input:  string = "engineers rock" pattern = "er";  Output:  true  Explanation:  All ’e’ in the input string are before all’ r’.  Input:  string = "engineers rock" pattern = "egr";  Output:  false  Explanation:  There are two ’e’ after’ g’ in the input string.  Input:  string = "engineers rock" pattern = "gsr";  Output:  false  Explanation:  There are one ’r’ before’ s’ in the input string. 

We have a solution to this problem, see OrderedDict () . The approach is very simple,

  • Create an OrderedDict of the input string that contains the characters of the input strings as the only key .
  • Now set the pointer at the beginning of the template string .
  • Now loop through the generated OrderedDict and match the keys to a single character of the template string, if the key and character match, then increment the pointer by 1.
  • If the template pointer reaches its end , this means that the line follows the order of the characters defined by the pattern, otherwise not.

# Function to check if a line is in order
# of characters defined by the template

from collections import OrderedDict

  

def checkOrder ( input , pattern):

 

# create empty OrderedDict

# the output will look like {& # 39; a & # 39 ;: no, & # 39; b & # 39 ;: no, & # 39; c & # 39 ;: no}

dict = OrderedDict.fromkeys ( input )

  

# traverse generated OrderedDict in parallel with

# string template to check if character order is

# same or not

  ptrlen = 0  

for key, value in dict . iteritems ():

  if (key = = pattern [ptrlen]):

ptrlen = ptrlen + 1

 

# check if we have a full move

# sample line

if (ptrlen = = ( len (pattern))):

return ’true’

  

  # if we break out of the for loop it means

# order does not match

return ’false’

  
# Driver program

if __ name__ = = "__ main__" :

input = ’engineers rock’  

pattern = ’egr’

  print checkOrder ( input , pattern)

Output:

 true 

This article is courtesy of Shashank Mishra (Gullu) . If you are as Python.Engineering and would like to contribute, you can also write an article using contribute.python.engineering or by posting an article contribute @ python.engineering. See my article appearing on the Python.Engineering homepage and help other geeks.

Please post comments if you find anything wrong or if you’d like to share more information on the topic discussed above.

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