How should I practice Longest Non-Repeating Substring?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Cisco phone screen problems in FastPrep.

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Problem · String

Longest Non-Repeating Substring

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Problem statement

Given a string s, return a longest contiguous substring that contains no repeated characters.

For this exercise, assume that when several longest valid substrings exist, you must return the one with the smallest starting index. If s is empty, return the empty string.

Function

longestUniqueSubstring(s: String) → String

Examples

Example 1

s = "abcabcbb"return = "abc"

The longest valid substrings have length 3. The earliest one is "abc", which starts at index 0.

Example 2

s = "pwwkew"return = "wke"

Both "wke" and "kew" have length 3. The leftmost tie rule selects "wke".

Example 3

s = "bbbbb"return = "b"

Every valid substring has length 1, so the first character is returned.

Example 4

s = ""return = ""

The empty string has no non-empty substring, so return "".

Constraints

0 <= s.length <= 200000
s contains lowercase English letters.