Add solution #126

Author: JoshCrozier

0126-word-ladder-ii.js

@@ -0,0 +1,76 @@
+/**
+ * 126. Word Ladder II
+ * https://leetcode.com/problems/word-ladder-ii/
+ * Difficulty: Hard
+ *
+ * A transformation sequence from word beginWord to word endWord using a dictionary wordList
+ * is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that:
+ * - Every adjacent pair of words differs by a single letter.
+ * - Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList.
+ * - sk == endWord
+ *
+ * Given two words, beginWord and endWord, and a dictionary wordList, return all the shortest
+ * transformation sequences from beginWord to endWord, or an empty list if no such sequence
+ * exists. Each sequence should be returned as a list of the words [beginWord, s1, s2, ..., sk].
+ */
+
+/**
+ * @param {string} beginWord
+ * @param {string} endWord
+ * @param {string[]} wordList
+ * @return {string[][]}
+ */
+var findLadders = function(beginWord, endWord, wordList) {
+  const set = new Set(wordList);
+  const queue = [beginWord];
+  const group = [];
+  let isEnd = false;
+
+  while (queue.length && !isEnd) {
+    group.push([...queue]);
+    const limit = queue.length;
+    for (let i = 0; i < limit && !isEnd; i++) {
+      const from = queue.shift();
+      for (const word of set) {
+        if (!isValid(from, word)) {
+          continue;
+        } else if (word === endWord) {
+          isEnd = true;
+          break;
+        }
+        queue.push(word);
+        set.delete(word);
+      }
+    }
+  }
+
+  if (!isEnd) {
+    return [];
+  }
+
+  const result = [[endWord]];
+  for (let i = group.length - 1; i >= 0; i--) {
+    const limit = result.length;
+    for (let j = 0; j < limit; j++) {
+      const path = result.shift();
+      for (const word of group[i]) {
+        if (!isValid(path[0], word)) {
+          continue;
+        }
+        result.push([word, ...path]);
+      }
+    }
+  }
+
+  return result;
+
+  function isValid(a, b) {
+    let count = 0;
+    for (let i = 0; i < a.length && count < 2; i++) {
+      if (a[i] !== b[i]) {
+        count++;
+      }
+    }
+    return count === 1;
+  }
+};

README.md

@@ -131,6 +131,7 @@
 123|[Best Time to Buy and Sell Stock III](./0123-best-time-to-buy-and-sell-stock-iii.js)|Hard|
 124|[Binary Tree Maximum Path Sum](./0124-binary-tree-maximum-path-sum.js)|Hard|
 125|[Valid Palindrome](./0125-valid-palindrome.js)|Easy|
+126|[Word Ladder II](./0126-word-ladder-ii.js)|Hard|
 127|[Word Ladder](./0127-word-ladder.js)|Hard|
 128|[Longest Consecutive Sequence](./0128-longest-consecutive-sequence.js)|Medium|
 129|[Sum Root to Leaf Numbers](./0129-sum-root-to-leaf-numbers.js)|Medium|