Word Ladder: coding question

Problem

You get a start word beginWord, an end word endWord and a list of words wordList. All the words have the same length.

A transformation sequence is a list of words that starts with beginWord and ends with endWord. Each word in the sequence differs from the word before it in exactly one letter.

Every word after beginWord must be in wordList. The word beginWord does not need to be in wordList.

Return the number of words in the shortest transformation sequence. If no sequence exists, return 0.

Example 1

Input:: beginWord = "cold", endWord = "warm", wordList = ["cord","card","ward","warm","word","worm"]
Output:: 5
Explanation:: One shortest sequence is "cold", "cord", "card", "ward", "warm". All 4 letters must change, so no sequence has fewer than 5 words.

Example 2

Input:: beginWord = "pin", endWord = "pot", wordList = ["pit","pat","pan"]
Output:: 0
Explanation:: The word "pot" is not in wordList, so no sequence can end with it.

Constraints

1 <= beginWord.length <= 10
endWord.length == beginWord.length
1 <= wordList.length <= 5000
wordList[i].length == beginWord.length
All the words have only lowercase English letters
beginWord != endWord
All the words in wordList are unique

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

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Amazon
Leetcode 127. Word Ladder
Reported Mar 19, 2026 · 6 source reports
MID_LEVEL, SENIOR
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Fan
Leetcode 127. Word Ladder
Reported Apr 15, 2026 · 1 source report
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Meta
Leetcode 127. Word Ladder
Reported Feb 2, 2026 · 5 source reports
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Microsoft
Leetcode 127. Word Ladder
Reported Mar 12, 2026 · 1 source report
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Problem

You get a start word beginWord, an end word endWord and a list of words wordList. All the words have the same length.

A transformation sequence is a list of words that starts with beginWord and ends with endWord. Each word in the sequence differs from the word before it in exactly one letter.

Every word after beginWord must be in wordList. The word beginWord does not need to be in wordList.

Return the number of words in the shortest transformation sequence. If no sequence exists, return 0.

Example 1

Input:: beginWord = "cold", endWord = "warm", wordList = ["cord","card","ward","warm","word","worm"]
Output:: 5
Explanation:: One shortest sequence is "cold", "cord", "card", "ward", "warm". All 4 letters must change, so no sequence has fewer than 5 words.

Example 2

Input:: beginWord = "pin", endWord = "pot", wordList = ["pit","pat","pan"]
Output:: 0
Explanation:: The word "pot" is not in wordList, so no sequence can end with it.

Constraints

1 <= beginWord.length <= 10
endWord.length == beginWord.length
1 <= wordList.length <= 5000
wordList[i].length == beginWord.length
All the words have only lowercase English letters
beginWord != endWord
All the words in wordList are unique

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

Word Ladder

Problem

Example 1

Example 2

Constraints

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Word Ladder

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