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FindLadders.java
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101 lines (94 loc) · 3.76 KB
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package serach;
import java.util.*;
public class FindLadders {
public List<List<String>> findLadders(String beginWord, String endWord, List<String> wordList) {
List<List<String>> ans = new ArrayList<>();
if (!wordList.contains(endWord)) {
return ans;
}
//利用BFS得到所有的邻居节点
HashMap<String, ArrayList<String>> map = new HashMap<>();
bfs(beginWord, endWord, wordList, map);
ArrayList<String> temp = new ArrayList<>();
//temp用来保存当前的路径
temp.add(beginWord);
findLaddersHelper(beginWord, endWord, map, temp, ans);
return ans;
}
private void findLaddersHelper(String beginWord, String endWord, HashMap<String, ArrayList<String>> map, ArrayList<String> temp, List<List<String>> ans) {
if (beginWord.equals(endWord)) {
ans.add(new ArrayList<>(temp));
return;
}
//得到所有的下一个的节点
ArrayList<String> neighbors = map.getOrDefault(beginWord, new ArrayList<String>());
for (String neighbor : neighbors) {
temp.add(neighbor);
findLaddersHelper(neighbor, endWord, map, temp, ans);
temp.remove(temp.size() - 1);
}
}
private void bfs(String beginWord, String endWord, List<String> wordList, HashMap<String, ArrayList<String>> map) {
Queue<String> queue = new LinkedList<>();
queue.offer(beginWord);
boolean isFound = false;
int depth = 0;
Set<String> dict = new HashSet<>(wordList);
Set<String> visited = new HashSet<>();
visited.add(beginWord);
while (!queue.isEmpty()) {
int size = queue.size();
depth++;
Set<String> subVisited = new HashSet<>();
for (int j = 0; j < size; j++) {
String temp = queue.poll();
//一次性得到所有的下一个的节点
ArrayList<String> neighbors = getNeighbors(temp, dict);
Iterator<String> it = neighbors.iterator();//把元素导入迭代器
while (it.hasNext()) {
String neighbor = it.next();
if (!visited.contains(neighbor)) {
if (neighbor.equals(endWord)) {
isFound = true;
}
queue.offer(neighbor);
subVisited.add(neighbor);
}else {
it.remove();
}
}
map.put(temp,neighbors);
}
visited.addAll(subVisited);
if (isFound){
break;
}
}
}
private ArrayList<String> getNeighbors(String node, Set<String> dict) {
ArrayList<String> res = new ArrayList<>();
char chs[] = node.toCharArray();
for (char ch = 'a'; ch <= 'z';ch++){
for (int i = 0; i < chs.length; i++) {
if (chs[i] == ch) continue;
char old_ch = chs[i];
chs[i] = ch;
if (dict.contains(String.valueOf(chs))){
res.add(String.valueOf(chs));
}
chs[i] = old_ch;
}
}
return res;
}
public static void main(String[] args) {
String beginWord = "hit";
String endWord = "cog";
List<String> wordList = new ArrayList<>();
String[] wordListArray = new String[]{"hot", "dot", "dog", "lot", "log", "cog"};
Collections.addAll(wordList, wordListArray);
FindLadders findLadders = new FindLadders();
List<List<String>> r = findLadders.findLadders(beginWord,endWord,wordList);
System.out.println(r.toString());
}
}