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‎Algorithms/0126.word-ladder-ii/README.md

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# [126. Word Ladder II](https://leetcode.com/problems/word-ladder-ii/)
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## 题目
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Given two words (beginWord and endWord), and a dictionary's word list, find **all shortest** transformation sequence(s) from beginWord to endWord, such that:
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1. Only one letter can be changed at a time
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1. Each transformed word must exist in the word list. Note that beginWord is not a transformed word.
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For example,
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```
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Given:
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beginWord = "hit"
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endWord = "cog"
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wordList = ["hot","dot","dog","lot","log","cog"]
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Return
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[
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["hit","hot","dot","dog","cog"],
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["hit","hot","lot","log","cog"]
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]
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```
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Note:
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1. Return an empty list if there is no such transformation sequence.
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1. All words have the same length.
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1. All words contain only lowercase alphabetic characters.
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1. You may assume no duplicates in the word list.
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1. You may assume beginWord and endWord are non-empty and are not the same.
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UPDATE (2017/1/20):
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The wordList parameter had been changed to a list of strings (instead of a set of strings). Please reload the code definition to get the latest changes.
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## 解题思路
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见程序注释

‎Algorithms/0126.word-ladder-ii/word-ladder-ii.go

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package Problem0126
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func findLadders(beginWord string, endWord string, words []string) [][]string {
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res := [][]string{}
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isUsed := map[string]bool{}
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transMap := map[string][]string{}
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for i := 0; i < len(words); i++ {
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if words[i] == beginWord {
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// Note that beginWord is not a transformed word.
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continue
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}
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if isTransable(words[i], beginWord) {
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transMap[beginWord] = append(transMap[beginWord], words[i])
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}
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for j := i + 1; j < len(words); j++ {
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if words[j] == beginWord {
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// Note that beginWord is not a transformed word.
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continue
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}
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a, b := words[i], words[j]
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if isTransable(a, b) {
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transMap[a] = append(transMap[a], b)
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transMap[b] = append(transMap[b], a)
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}
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}
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}
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minLen := 1<<63 - 1
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var dfs func(string, []string, int)
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dfs = func(word string, path []string, idx int) {
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tempLen := idx + 1
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if minLen < tempLen {
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return
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}
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for _, w := range transMap[word] {
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if isUsed[w] {
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continue
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}
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path[idx] = w
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if w == endWord {
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temp := make([]string, tempLen)
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copy(temp, path)
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if minLen > tempLen {
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minLen = tempLen
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res = [][]string{temp}
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} else {
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// minLen == tempLen
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res = append(res, temp)
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}
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return
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}
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isUsed[w] = true
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dfs(w, path, idx+1)
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isUsed[w] = false
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}
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}
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path := make([]string, len(words)*2)
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path[0] = beginWord
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dfs(beginWord, path, 1)
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return res
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}
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func isTransable(a, b string) bool {
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diff := false
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for i := range a {
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if a[i] != b[i] {
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if !diff {
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diff = true
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} else {
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return false
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}
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}
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}
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return true
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}

‎Algorithms/0126.word-ladder-ii/word-ladder-ii_test.go

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package Problem0126
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import (
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"fmt"
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"testing"
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"github.com/stretchr/testify/assert"
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)
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func Test_Problem0126(t *testing.T) {
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ast := assert.New(t)
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// tcs is testcase slice
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tcs := []struct {
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beginWord string
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endWord string
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wordList []string
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ans [][]string
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}{
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{
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"qa",
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"sq",
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[]string{"si", "go", "se", "cm", "so", "ph", "mt", "db", "mb", "sb", "kr", "ln", "tm", "le", "av", "sm", "ar", "ci", "ca", "br", "ti", "ba", "to", "ra", "fa", "yo", "ow", "sn", "ya", "cr", "po", "fe", "ho", "ma", "re", "or", "rn", "au", "ur", "rh", "sr", "tc", "lt", "lo", "as", "fr", "nb", "yb", "if", "pb", "ge", "th", "pm", "rb", "sh", "co", "ga", "li", "ha", "hz", "no", "bi", "di", "hi", "qa", "pi", "os", "uh", "wm", "an", "me", "mo", "na", "la", "st", "er", "sc", "ne", "mn", "mi", "am", "ex", "pt", "io", "be", "fm", "ta", "tb", "ni", "mr", "pa", "he", "lr", "sq", "ye"},
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[][]string{
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[]string{"qa", "ba", "be", "se", "sq"},
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[]string{"qa", "ba", "bi", "si", "sq"},
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[]string{"qa", "ba", "br", "sr", "sq"},
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[]string{"qa", "ca", "cm", "sm", "sq"},
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[]string{"qa", "ca", "co", "so", "sq"},
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[]string{"qa", "la", "ln", "sn", "sq"},
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[]string{"qa", "la", "lt", "st", "sq"},
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[]string{"qa", "ma", "mb", "sb", "sq"},
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[]string{"qa", "pa", "ph", "sh", "sq"},
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[]string{"qa", "ta", "tc", "sc", "sq"},
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[]string{"qa", "fa", "fe", "se", "sq"},
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[]string{"qa", "ga", "ge", "se", "sq"},
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[]string{"qa", "ha", "he", "se", "sq"},
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[]string{"qa", "la", "le", "se", "sq"},
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[]string{"qa", "ma", "me", "se", "sq"},
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[]string{"qa", "na", "ne", "se", "sq"},
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[]string{"qa", "ra", "re", "se", "sq"},
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[]string{"qa", "ya", "ye", "se", "sq"},
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[]string{"qa", "ca", "ci", "si", "sq"},
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[]string{"qa", "ha", "hi", "si", "sq"},
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[]string{"qa", "la", "li", "si", "sq"},
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[]string{"qa", "ma", "mi", "si", "sq"},
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[]string{"qa", "na", "ni", "si", "sq"},
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[]string{"qa", "pa", "pi", "si", "sq"},
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[]string{"qa", "ta", "ti", "si", "sq"},
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[]string{"qa", "ca", "cr", "sr", "sq"},
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[]string{"qa", "fa", "fr", "sr", "sq"},
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[]string{"qa", "la", "lr", "sr", "sq"},
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[]string{"qa", "ma", "mr", "sr", "sq"},
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[]string{"qa", "fa", "fm", "sm", "sq"},
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[]string{"qa", "pa", "pm", "sm", "sq"},
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[]string{"qa", "ta", "tm", "sm", "sq"},
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[]string{"qa", "ga", "go", "so", "sq"},
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[]string{"qa", "ha", "ho", "so", "sq"},
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[]string{"qa", "la", "lo", "so", "sq"},
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[]string{"qa", "ma", "mo", "so", "sq"},
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[]string{"qa", "na", "no", "so", "sq"},
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[]string{"qa", "pa", "po", "so", "sq"},
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[]string{"qa", "ta", "to", "so", "sq"},
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[]string{"qa", "ya", "yo", "so", "sq"},
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[]string{"qa", "ma", "mn", "sn", "sq"},
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[]string{"qa", "ra", "rn", "sn", "sq"},
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[]string{"qa", "ma", "mt", "st", "sq"},
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[]string{"qa", "pa", "pt", "st", "sq"},
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[]string{"qa", "na", "nb", "sb", "sq"},
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[]string{"qa", "pa", "pb", "sb", "sq"},
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[]string{"qa", "ra", "rb", "sb", "sq"},
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[]string{"qa", "ta", "tb", "sb", "sq"},
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[]string{"qa", "ya", "yb", "sb", "sq"},
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[]string{"qa", "ra", "rh", "sh", "sq"},
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[]string{"qa", "ta", "th", "sh", "sq"},
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},
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},
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{
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"hit",
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"cog",
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[]string{"hot", "dot", "dog", "lot", "log"},
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[][]string{},
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},
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{
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"hot",
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"dog",
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[]string{"hot", "dog", "dot"},
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[][]string{
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[]string{"hot", "dot", "dog"},
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},
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},
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{
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"hit",
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"cog",
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[]string{"hot", "dot", "dog", "lot", "log", "cog"},
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[][]string{
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[]string{"hit", "hot", "dot", "dog", "cog"},
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[]string{"hit", "hot", "lot", "log", "cog"},
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},
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},
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// 可以多个 testcase
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}
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for _, tc := range tcs {
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fmt.Printf("~~%v~~\n", tc)
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ast.Equal(tc.ans, findLadders(tc.beginWord, tc.endWord, tc.wordList), "输入:%v", tc)
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}
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}

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