Write a function that takes in two strings and returns true if the second string is substring of the first, and false otherwise.
Understand what the interviewer is asking for by using test cases and questions about the problem.
- Established a set (2-3) of test cases to verify their own solution later.
- Established a set (1-2) of edge cases to verify their solution handles complexities.
- Have fully understood the problem and have no clarifying questions.
- Have you verified any Time/Space Constraints for this problem?
Run through a set of example cases:
HAPPY CASE
Input: laboratory, rat
Output: true
Input: cat, meow
Output: false
EDGE CASE
Input: "CATDOG", ""
Output: True
Match what this problem looks like to known categories of problems, e.g. Linked List or Dynamic Programming, and strategies or patterns in those categories.
For Strings, common solution patterns include:
Plan the solution with appropriate visualizations and pseudocode.
General Idea: Loop through the first string for an initial match. If we find one, check that match for a full substring match.
1) Edge Check
2) Loop through the first string
3) Find a match to the first character of the second string
4) While there is a match, loop through both strings in parallel to ensure
the match
5) If there is an entire match to the second string, return True (there is a
substring)
6) If the match breaks, continue searching the first string for an initial
character match
7) If we make it to the end of the first string without a full match, there
is no substring match -- return False
⚠️ Common Mistakes
Implement the code to solve the algorithm.
def substring(large_str, potential_substr):
substr_len = len(potential_substr)
# iterate through larger str for its length minus substr length
for i in range(len(large_str) - substr_len):
# iterate through potential substr
for j in range(substr_len):
# if chars match in both string
if large_str[i + j] == potential_substr[j]:
# if at the end of substring, return true
if j == (substr_len - 1):
return True
# else do nothing and continue looping
else:
break
# did not find substring
return False
Review the code by running specific example(s) and recording values (watchlist) of your code's variables along the way.
Evaluate the performance of your algorithm and state any strong/weak or future potential work.
O(n*m)
, where n
: length of first string, m
: length of second string