Word Ladder

Description

Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that:

1. Only one letter can be changed at a time.
2. Each transformed word must exist in the word list.

Note:

• Return 0 if there is no such transformation sequence.
• All words have the same length.
• All words contain only lowercase alphabetic characters.
• You may assume no duplicates in the word list.
• You may assume beginWord and endWord are non-empty and are not the same.

Example 1:

Input:
beginWord = "hit",
endWord = "cog",
wordList = ["hot","dot","dog","lot","log","cog"]
Output: 5
Explanation: As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog",
return its length 5.

Example 2:

Input:
beginWord = "hit"
endWord = "cog"
wordList = ["hot","dot","dog","lot","log"]
Output: 0
Explanation: The endWord "cog" is not in wordList, therefore no possible transformation.

Solution(javascript)

const ladderLength = function (beginWord, endWord = '', wordList = []) {
  const distance = (a = '', b = '') => {
    let count = 0
    for (let index = 0; index < b.length; index++) {
      if (a[index] !== b[index]) {
        count += 1
      }
    }
    return count === 1
  }
  let current = [beginWord]
  const visited = {
  }
  let count = 1
  while (current.length > 0) {
    const next = []
    for (const word of current) {
      if (word === endWord) {
        return count
      }
      if (!visited[word]) {
        next.push(...wordList.filter(word2 => distance(word, word2) && !visited[word2]))
      }
      visited[word] = true
    }
    count += 1
    current = next
  }
  return 0
}