leetcode 126. Word Ladder II

leetcode 126. Word Ladder II   写这一题 真的非常适合复习bfs与dfs啊

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Set;

public class Solution{
public static void main(String[] args){
Solution s = new Solution();
List<String> wordList = new ArrayList<String>();
wordList.add("hot");
wordList.add("dot");
wordList.add("dog");
wordList.add("lot");
wordList.add("log");
wordList.add("cog");
// wordList.add("cot");
List<List<String>> res = s.findLadders("hit", "cog", wordList);
System.out.println(res);
}

public List<List<String>> findLadders(String beginWord, String endWord,
List<String> wordList) {
HashSet<String> dict = new HashSet<String>(wordList);
List<List<String>> res = new ArrayList<List<String>>();
Queue<String> queue = new LinkedList<String>();
Map<String, List<String>> strmap = new HashMap<String, List<String>>();
Map<String, Integer> distance = new HashMap<String, Integer>();
for(String str:dict){
strmap.put(str, new ArrayList<String>());
}
strmap.put(beginWord, new ArrayList<String>());
queue.add(beginWord);
queue.remove(endWord);
int string_size = beginWord.length();
int final_layer = Integer.MAX_VALUE;
int cur_layer = 0;
distance.put(beginWord, 0);
while(!queue.isEmpty()){
String cur = queue.poll();
char[] new_str = cur.toCharArray();
if(distance.get(cur)>=final_layer){
break;
}
boolean isFound = false;
for(int i=0;i<string_size;i++){
for(char c='a';c<='z';c++){
char origin_char = cur.charAt(i);
if(c==origin_char) continue;
new_str[i] = c;
String new_s = String.valueOf(new_str);
if(dict.contains(new_s)){
if(new_s.equals("log")){
int n = 1;
}
strmap.get(cur).add(new_s);
if(!distance.containsKey(new_s)){
distance.put(new_s, distance.get(cur)+1);
if(new_s.equals(endWord)){
final_layer = distance.get(cur)+1;
System.out.println("final_layer "+final_layer);
}else{
queue.offer(new_s);
}
}
}
new_str[i] = origin_char;
}
}
}
dfs(strmap,beginWord,endWord,res,final_layer,
new ArrayList<String>(),distance);
return res;
}

private ArrayList<String> getNeighbors(String node, Set<String> dict) {
ArrayList<String> res = new ArrayList<String>();
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 void dfs(Map<String, List<String>> strmap, String beginWord,
String endWord, List<List<String>> res,
int final_layer, List<String> path,Map<String, Integer> distance){
path.add(beginWord);
if(path.size()==final_layer+1){
if(beginWord.equals(endWord)){
res.add(new ArrayList<String>(path));
// System.out.println(res);
}
// path.clear();
// System.out.println(res);
path.remove(path.size()-1);
return;
}

for(String s: strmap.get(beginWord)){
if((distance.get(s)==distance.get(beginWord)+1))
dfs(strmap,s,endWord,res,final_layer,path,distance);
}
path.remove(path.size()-1); // backtrack
}
}