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

Oct 31, 2020 #### 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: 7print(findFirstOccurrence(s, occ2)) # display: -1``

Younes Derfoufi
my-courses.net