Final exam — String
Three unseen problems (not covered in the lessons) to test whether you leave this section able to solve any problem of the topic: one easy, one medium and one hard. Some test cases are hidden — like the real LeetCode. Solve in Python or JavaScript.
First Unique Character in a String
Given a string s, return the index of the first character that does not repeat. If there is none, return -1.
Example: s = "leetcode" → 0 (the 'l' is the first one that appears exactly once). s = "aabb" → -1.
Find All Anagrams in a String
Given two strings s and p, return a list of the starting indices of all anagrams of p within s (in increasing order).
Example: s = "cbaebabacd", p = "abc" → [0, 6] (the slices "cba" and "bac" are anagrams of "abc").
Longest Valid Parentheses
Given a string s containing only ( and ), return the length of the longest substring of valid parentheses (correctly closed).
Example: s = ")()())" → 4 (the substring "()()"). s = "(()" → 2.