Alien Dictionary: coding question

Problem

An alien language uses the lowercase English letters, but you do not know the order of the letters. You get a list words from the dictionary of this language.

The list words is in the lexical order of the alien language. Lexical order compares two words letter by letter, and the first different letter decides the order. A prefix is a part at the start of a word. If one word is a prefix of the other word, the shorter word comes first.

Return a string with each different letter of words one time, in the alien order. If more than one order is correct, return any of them.

If no order of the letters puts words in lexical order, return an empty string "".

Example 1

Input:: words = ["ca","cb","ac","bb"]
Output:: "cab"
Explanation:: From "ca" and "cb", the letter a comes before b. From "cb" and "ac", the letter c comes before a.

Example 2

Input:: words = ["x","z","x"]
Output:: ""
Explanation:: The list needs x before z and also z before x. No order of the letters is correct.

Example 3

Input:: words = ["pqr","pq"]
Output:: ""
Explanation:: The word "pq" is a prefix of "pqr", so "pq" must come first in every order.

Constraints

1 <= words.length <= 100
1 <= words[i].length <= 100
words[i] has only lowercase English letters

SysRound wrote this statement. A reference solution checks every example.

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Problem

An alien language uses the lowercase English letters, but you do not know the order of the letters. You get a list words from the dictionary of this language.

Return a string with each different letter of words one time, in the alien order. If more than one order is correct, return any of them.

If no order of the letters puts words in lexical order, return an empty string "".

Example 1

Input:: words = ["ca","cb","ac","bb"]
Output:: "cab"
Explanation:: From "ca" and "cb", the letter a comes before b. From "cb" and "ac", the letter c comes before a.

Example 2

Input:: words = ["x","z","x"]
Output:: ""
Explanation:: The list needs x before z and also z before x. No order of the letters is correct.

Example 3

Input:: words = ["pqr","pq"]
Output:: ""
Explanation:: The word "pq" is a prefix of "pqr", so "pq" must come first in every order.

Constraints

1 <= words.length <= 100
1 <= words[i].length <= 100
words[i] has only lowercase English letters

SysRound wrote this statement. A reference solution checks every example.

Alien Dictionary

Problem

Example 1

Example 2

Example 3

Constraints

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Alien Dictionary

Problem

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Example 2

Example 3

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