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#600 #3

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126
Apr 26, 2017
156b6c2
Merge pull request #1 from tianheng/126
tianheng Apr 26, 2017
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162 changes: 74 additions & 88 deletions #126
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Original file line number Diff line number Diff line change
@@ -1,89 +1,75 @@
126. Word Ladder II

Given two words (beginWord and endWord), and a dictionary's word list, find all shortest transformation sequence(s) from beginWord to endWord, such that:

Only one letter can be changed at a time
Each transformed word must exist in the word list. Note that beginWord is not a transformed word.
For example,

Given:
beginWord = "hit"
endWord = "cog"
wordList = ["hot","dot","dog","lot","log","cog"]

Return
[
["hit","hot","dot","dog","cog"],
["hit","hot","lot","log","cog"]
]


public class Solution {

public List<List<String>> findLadders(String beginWord, String endWord, List<String> wordList) {
Map<String, Integer> map = new HashMap<>();
Map<String, Set<String>> neighbors = new HashMap<>();
neighbors.put(beginWord, new HashSet<>());
map.put(beginWord, -1);
Set<String> wordSet = new HashSet<>();
for(String word : wordList){
wordSet.add(word);
map.put(word, -1);
neighbors.put(word, new HashSet<>());
}
int distance = 0;
boolean found = false;
Queue<String> queue = new LinkedList<>();
queue.offer(beginWord);
while(!queue.isEmpty()){
int len = queue.size();
for(int i = 0; i < len; i++){
String curWord = queue.poll();
if(map.get(curWord) == -1 || map.get(curWord) > distance){
map.put(curWord, distance);
}
if(curWord.equals(endWord)){
found = true;
}
for(int j = 0; j < curWord.length(); j++){
char[] arr = curWord.toCharArray();
for(char c = 'a'; c <= 'z'; c++){
if(c != arr[j]){
arr[j] = c;
}
String newWord = new String(arr);
if(wordSet.contains(newWord)){
if(map.get(newWord) == -1){
queue.offer(newWord);
neighbors.get(curWord).add(newWord);
}
}
}
}
}
if(found) break;
distance++;
}
List<List<String>> wraplist = new ArrayList<>();
dfs(map, neighbors, new ArrayList<>(), wraplist, beginWord, endWord);
return wraplist;
}

public void dfs(Map<String, Integer> map, Map<String, Set<String>> neighbors, List<String> sublist, List<List<String>> wraplist, String curWord, String endWord){

if(curWord.equals(endWord)){
sublist.add(curWord);
wraplist.add(new ArrayList<>(sublist));
sublist.remove(sublist.size() - 1);
return;
}

for(String neighbor : neighbors.get(curWord)){
sublist.add(curWord);
if(map.get(neighbor) == map.get(curWord) + 1){
dfs(map, neighbors, sublist, wraplist, neighbor, endWord);
}
sublist.remove(sublist.size() - 1);
}
}
public class Solution {

public List<List<String>> findLadders(String beginWord, String endWord, List<String> wordList) {
Set<String> wordDict = new HashSet<>(wordList);
Map<String, Integer> distances = new HashMap<>();
Map<String, Set<String>> graph = new HashMap<>();

wordDict.add(beginWord);
for(String word : wordDict){
graph.put(word, new HashSet<>());
}

Queue<String> queue = new LinkedList<>();
queue.offer(beginWord);
distances.put(beginWord, 0);
boolean found = false;

while(!queue.isEmpty()){
String curWord = queue.poll();
int cur_distance = distances.get(curWord);
Set<String> neighbors = getNeighbors(curWord, wordDict);
for(String neighbor : neighbors){
graph.get(curWord).add(neighbor);
if(!distances.containsKey(neighbor)){
distances.put(neighbor, cur_distance + 1);
queue.offer(neighbor);
}
}
if(curWord.equals(endWord)){
found = true;
break;
}
}

List<List<String>> wraplist = new ArrayList<>();
if(!found) return wraplist;
findPath(distances, graph, new ArrayList<>(), wraplist, endWord, beginWord);
return wraplist;
}

public Set<String> getNeighbors(String curWord, Set<String> wordSet){
Set<String> neighbors = new HashSet<>();
for(int j = 0; j < curWord.length(); j++){
char[] arr = curWord.toCharArray();
for(char c = 'a'; c <= 'z'; c++){
if(c == arr[j]) continue;
arr[j] = c;
String newWord = new String(arr);
if(wordSet.contains(newWord)){
neighbors.add(newWord);
}
}
}
return neighbors;
}

public void findPath(Map<String, Integer> distances, Map<String, Set<String>> graph, List<String> sublist, List<List<String>> wraplist, String curWord, String startWord){

sublist.add(curWord);
if(curWord.equals(startWord)){
List<String> res = new ArrayList<>(sublist);
Collections.reverse(res);
wraplist.add(res);
sublist.remove(sublist.size() - 1);
return;
}

for(String neighbor : graph.get(curWord)){
if(distances.get(neighbor) == distances.get(curWord) - 1){
findPath(distances, graph, sublist, wraplist, neighbor, startWord);
}
}
sublist.remove(sublist.size() - 1);
}
}