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 –
Python3
string = "LazyroarforLazyroar"print(string.count("Lazyroar")) |
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 –
Python3
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 Codestring = "LazyroarforLazyroar"print(CountOccurrences(string, "Lazyroar")) |
3
Time complexity: O(n), where n is length of string.
Auxiliary Space: O(1)
