127. Word Ladder

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Problem

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:

Note:

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

/**
 * @param {string} beginWord
 * @param {string} endWord
 * @param {string[]} wordList
 * @return {number}
 */
var ladderLength = function(beginWord, endWord, wordList) {
  var wordSet = new Set(wordList);
  var queue = [];
  var step = 0;
  var word = '';
  var len = 0;
  var i = 0;

  pushNextWord(beginWord, queue, wordSet);
  step = 2;

  while (len = queue.length) {
    for (i = 0; i < len; i++) {
      word = queue.shift();
      if (word === endWord) return step;
      pushNextWord(word, queue, wordSet);
    }
    step++;
  }

  return 0;
};

var pushNextWord = function (word, queue, wordSet) {
  var start = 'a'.charCodeAt(0);
  var len = word.length;
  var str = '';

  wordSet.delete(word);

  for (var i = 0; i < len; i++) {
    for (var j = 0; j < 26; j++) {
      str = word.substr(0, i) + String.fromCharCode(j + start) + word.substr(i + 1);

      if (wordSet.has(str)) {
        queue.push(str);
        wordSet.delete(str);
      }
    }
  }
};

Explain:

nope.

Complexity: