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Python | Count overlapping substring in a given string

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  • Last Updated : 20 Apr, 2020
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Given a string and a sub-string, the task is to get the count of overlapping substring from the given string.

Note that in Python, the count() function returns the number of substrings in a given string, but it does not give correct results when two occurrences of the substring overlap. Consider this example –




string = "GeeksforGeeksforGeeksforGeeks"
  
print(string.count("GeeksforGeeks"))

Output:

2

The output we got here is 2, but the expected output is 3 since we also wanted to count the occurrence of overlapped sub-string.

In order to solve this problem, we can use find() function in Python. It returns the start position of the first occurrence of substring in the given string, then we increment this position by 1 and continue the search from that position till the end of the string.

Below is the implementation –




def CountOccurrences(string, substring):
  
    # Initialize count and start to 0
    count = 0
    start = 0
  
    # Search through the string till
    # we reach the end of it
    while start < len(string):
  
        # Check if a substring is present from
        # 'start' position till the end
        pos = string.find(substring, start)
  
        if pos != -1:
            # If a substring is present, move 'start' to
            # the next position from start of the substring
            start = pos + 1
  
            # Increment the count
            count += 1
        else:
            # If no further substring is present
            break
    # return the value of count
    return count
  
# Driver Code
string = "GeeksforGeeksforGeeksforGeeks"
print(CountOccurrences(string, "GeeksforGeeks"))

Output:

3

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