Level 3: Strings and dates · Exercise 45 of 76 · Free

Longest stretch without a repeat

A JavaScript exercise from Scriptdrill. Solve it with a code editor in your browser that runs your function against example and hidden tests, and it is checked the moment you submit.

The task

Return the length of the longest substring of `s` in which no character appears twice. A substring is a run of neighboring characters: in `"pwwkew"` the answer is 3 (`"wke"`), not 4, because `"pwke"` skips a character. An empty string gives 0.

What this exercise teaches

The window always holds a stretch without repeats. A repeated character only matters if its earlier copy is still inside the window, which is why the start is set with Math.max: without it, an old position can drag the start backwards, as in abba.

A hint if you get stuck

Slide a window over the string. Remember the last index of every character in a `Map`. When the current character was last seen inside the window, move the start of the window to just after that position, and never move it backwards.