Python | Check order of character in string using OrderedDict( ) - GeeksforGeeks

23 Nov, 2020
Given an input string and a pattern, check if characters in the input string follows the same order as determined by characters present in the pattern. Assume there won’t be any duplicate characters in the pattern.
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 existing solution for this problem, please refer Check if string follows order of characters defined by a pattern or not | Set 1. Here we solve this problem quickly in python using OrderedDict(). Approach is very simple,
Create an OrderedDict of input string which contains characters of input strings as Key only.
Now set a pointer at the start of pattern string.
Now traverse generated OrderedDict and match keys with individual character of pattern string, if key and character matches with each other then increment pointer by 1.
If pointer of pattern reaches it’s end that means string follows order of characters defined by a pattern otherwise not.
# Function to check if string follows order of # characters defined by a pattern from collections import OrderedDict   def checkOrder(input, pattern):           # create empty OrderedDict     # output will be like {'a': None,'b': None, 'c': None}     dict = OrderedDict.fromkeys(input)       # traverse generated OrderedDict parallel with     # pattern string to check if order of characters     # are same or not     ptrlen = 0    for key,value in dict.items():         if (key == pattern[ptrlen]):             ptrlen = ptrlen + 1                  # check if we have traverse complete         # pattern string         if (ptrlen == (len(pattern))):             return 'true'      # if we come out from for loop that means     # order was mismatched     return 'false'  # Driver program if __name__ == "__main__":     input = 'engineers rock'    pattern = 'egr'    print (checkOrder(input,pattern)) 
Output:
true

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