Shop/SDET Interview Kit

What you'll be able to do

• Solve the string, array, stack, tree and graph problems SDET loops actually use
• Talk through complexity and edge cases like an SDET — not just a developer
• Answer framework-design and test-infrastructure questions with real trade-offs
• Deliver a take-home that reviewers rate highly

Free sample · Q7, Python solution

Longest substring without repeating characters

Sliding window: move the right edge, and when a character repeats inside the window, jump the left edge past its last position. O(n) time.

def longest_unique_substring(s: str) -> int:
    last = {}
    left = best = 0
    for right, ch in enumerate(s):
        if ch in last and last[ch] >= left:
            left = last[ch] + 1
        last[ch] = right
        best = max(best, right - left + 1)
    return best