The key move is building a rank lookup from the order string first, then just comparing adjacent word pairs.
First, map each character in the custom alphabet to its rank (e.g., index in the alphabet string) to enable O(1) comparisons. Then, iterate through adjacent word pairs and compare them character by character using the custom ranks; if a mismatch is found, ensure the first word's character has a lower rank. Also handle the edge case where one word is a prefix of the other: the shorter word must come first.
Pro tip: Clarify whether the custom alphabet contains all 26 letters or just a subset, and whether words can contain characters outside the alphabet. Handling these edge cases upfront shows thoroughness and prevents incorrect assumptions.
Ask if the custom alphabet includes all letters, if words can have characters not in the alphabet, and if the list can be empty or have one word. Confirm that 'sorted' means non-decreasing order.
Create a hash map or array that maps each character in the custom alphabet to its index (rank). This allows O(1) lookups during comparisons.
Iterate through the list from i=0 to n-2. For each pair (words[i], words[i+1]), compare them character by character using the rank map to determine the correct order.
If a mismatch occurs, check if rank of char from first word < rank of char from second word; if not, return false. If one word is a prefix of the other, ensure the shorter word comes first; otherwise, return false.
If all adjacent pairs are in order, return true. Discuss time complexity O(N*L) where N is number of words and L is max word length, and space complexity O(1) for the rank map (since alphabet size is constant).
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