Longest Substring Without Repeated Characters

Question

The question asks the candidate to find the length of the longest substring without repeating characters from a given string.

Codemia · Accepted Answer

To solve the problem of finding the longest substring without repeating characters, I will use the sliding window technique combined with a hashmap. The sliding window allows us to expand and contract our substring dynamically while the hashmap will help track the characters and their indices.

1. Initialize a hashmap to store the last index of each character.
2. Use two pointers, `start` and `end`, to represent the current window of characters.
3. Iterate through the string with the `end` pointer:
   - If the character at `end` is already in the hashmap and its stored index is greater than or equal to `start`, update `start` to the index after the last occurrence of that character.
   - Update the hashmap with the current index of the character.
   - Calculate the length of the current substring and update the maximum length if necessary.
4. Return the maximum length found.

The time complexity of this algorithm is O(n) because we traverse the string once, and each character is processed in constant time due to the hashmap operations. The space complexity is O(min(n, m)), where n is the length of the string and m is the character set size.

```python
def length_of_longest_substring(s: str) -> int:
    char_index_map = {}
    max_length = 0
    start = 0

for end in range(len(s)):
        if s[end] in char_index_map:
            start = max(start, char_index_map[s[end]] + 1)
        char_index_map[s[end]] = end
        max_length = max(max_length, end - start + 1)

return max_length
```
This implementation efficiently calculates the length of the longest substring without repeating characters.

Consider edge cases such as an empty string, a string with all unique characters, or a string where all characters are the same. The algorithm should handle these cases correctly, returning 0 for an empty string, the length of the string for unique characters, and 1 for strings with all identical characters.

Longest Substring Without Repeated Characters

Cisco

What the Interviewer Expects

Key Topics to Cover

How to Approach This

Possible Follow-up Questions

Sharpen Your Skills on Codemia

Sample Answer

Approach

Algorithm

Submit Your Answer

Cisco Software Engineer Interview Guide

Related Questions

Binary Search on graph

Count kth largest element in array

Find connected components in string

Merge Three Sorted strings

Binary Search on string