Solution Exercise 77: python algorithm to find the first index of a given occurrence within a given string

Exercise 77

Write a Python algorithm which determines the first index of an existing occurrence within a given string s without using any predefined method as find() or rfind()... The algorithm must return -1 if the occorrence does not exist within the string s. Example if s = "Python programming language", and occ = "prog" the algorithm return 7

Solution

def findFirstOccurrence(s , occ):
    # getting the length of the occurrence occ and the len of the string s 
    m = len(occ)
    n = len(s)

    # initialize index 
    index = -1
    # searching the occurrence occ within the string s
    for i in range(0 , n-m):
        if s[i : m + i] == occ:
            index = i
            break
    return index

# Example:
s = "Python programming language"
occ1 = "prog"
occ2 = "algorithm"
print(findFirstOccurrence(s, occ1)) # display: 7
print(findFirstOccurrence(s, occ2)) # display: -1