word-ladder-test.js

/**
 * Problem: Word Ladder
 *
 * Given a `beginWord`, an `endWord`, and a list of `wordList`:
 * Transform `beginWord` into `endWord` by changing **only one letter at a time**,
 * and each intermediate word must exist in the `wordList`.
 *
 * Return the **minimum number of transformations** required.
 * If no such sequence exists, return 0.
 *
 * Note: You may assume beginWord and endWord are lowercase and of the same length.
 *
 * Example:
 * Input:
 *   beginWord = "hit"
 *   endWord = "cog"
 *   wordList = ["hot","dot","dog","lot","log","cog"]
 * Output: 5
 * Explanation: "hit" → "hot" → "dot" → "dog" → "cog"
 *
 * Why BFS?
 * Because you're looking for the **shortest transformation** → use BFS to explore word levels.
 */
function wordLadder(beginWord, endWord, wordList) {
    // 1. Convert wordList to a Set for O(1) lookups
    // 2. Use a queue to store current word and step count
    // 3. While queue is not empty:
    //    a. For each word in the queue:
    //        i. If word is endWord, return step count
    //       ii. Generate all valid one-letter transformations
    //      iii. If transformation is in wordSet, enqueue it and remove from wordSet
    // 4. If queue empties with no result, return 0
}
function testWordLadder() {
    const begin = "hit";
    const end = "cog";
    const wordList = ["hot","dot","dog","lot","log","cog"];
    const expected = 5;

    const actual = wordLadder(begin, end, wordList);
    console.log(actual === expected ? "✅ PASS" : `❌ FAIL (got ${actual}, expected ${expected})`);
}

testWordLadder();