Transform beginWord into endWord by changing one letter per step. Every word after the start must be in wordList. Return the smallest number of words in such a sequence, or zero if impossible.
Example 1 One-letter transformations among the start and dictionary words. Start: cat; target: dog. One-letter transformations among the start and dictionary words. Start: cat; target: dog. Vertices: node 0: cat, node 1: cot, node 2: cog, node 3: dog, node 4: dat, node 5: dot. Edges: node 0 (cat) — node 1 (cot); node 0 (cat) — node 4 (dat); node 1 (cot) — node 2 (cog); node 1 (cot) — node 5 (dot); node 2 (cog) — node 3 (dog); node 3 (dog) — node 5 (dot); node 4 (dat) — node 5 (dot). cat cot cog dog dat dot One-letter transformations among the start and dictionary words. Start: cat; target: dog. beginWord = "cat"
endWord = "dog"
wordList = ["cot","cog","dog","dat","dot"]4Explanation cat->cot->cog->dog changes one letter per step and uses four words.
Example 2 One-letter transformations among the start and dictionary words. Start: cat; target: dog (absent from dictionary). One-letter transformations among the start and dictionary words. Start: cat; target: dog (absent from dictionary). Vertices: node 0: cat, node 1: cot, node 2: cog. Edges: node 0 (cat) — node 1 (cot); node 1 (cot) — node 2 (cog). cat cot cog One-letter transformations among the start and dictionary words. Start: cat; target: dog (absent from dictionary). beginWord = "cat"
endWord = "dog"
wordList = ["cot","cog"]0Explanation dog is absent from the dictionary, preventing a valid final word.
Example 3 One-letter transformations among the start and dictionary words. Start: a; target: c. One-letter transformations among the start and dictionary words. Start: a; target: c. Vertices: node 0: a, node 1: b, node 2: c. Edges: node 0 (a) — node 1 (b); node 0 (a) — node 2 (c); node 1 (b) — node 2 (c). a b c One-letter transformations among the start and dictionary words. Start: a; target: c. beginWord = "a"
endWord = "c"
wordList = ["a","b","c"]2Explanation a changes directly to c, using two words.
Constraints Words are lowercase and have equal length 1..10 beginWord differs from endWord At most 5000 distinct dictionary words Function contract ladderLengthArguments: json, json, json
