|
|
package class26;
|
|
|
|
|
|
import java.util.ArrayList;
|
|
|
import java.util.HashMap;
|
|
|
import java.util.HashSet;
|
|
|
import java.util.LinkedList;
|
|
|
import java.util.List;
|
|
|
import java.util.Queue;
|
|
|
|
|
|
// 本题测试链接 : https://leetcode.com/problems/word-ladder-ii/
|
|
|
public class Code04_WordLadderII {
|
|
|
|
|
|
public static List<List<String>> findLadders(String start, String end, List<String> list) {
|
|
|
list.add(start);
|
|
|
HashMap<String, List<String>> nexts = getNexts(list);
|
|
|
HashMap<String, Integer> fromDistances = getDistances(start, nexts);
|
|
|
List<List<String>> res = new ArrayList<>();
|
|
|
if (!fromDistances.containsKey(end)) {
|
|
|
return res;
|
|
|
}
|
|
|
HashMap<String, Integer> toDistances = getDistances(end, nexts);
|
|
|
LinkedList<String> pathList = new LinkedList<>();
|
|
|
getShortestPaths(start, end, nexts, fromDistances, toDistances, pathList, res);
|
|
|
return res;
|
|
|
}
|
|
|
|
|
|
public static HashMap<String, List<String>> getNexts(List<String> words) {
|
|
|
HashSet<String> dict = new HashSet<>(words);
|
|
|
HashMap<String, List<String>> nexts = new HashMap<>();
|
|
|
for (int i = 0; i < words.size(); i++) {
|
|
|
nexts.put(words.get(i), getNext(words.get(i), dict));
|
|
|
}
|
|
|
return nexts;
|
|
|
}
|
|
|
|
|
|
// word, 在表中，有哪些邻居，把邻居们，生成list返回
|
|
|
public static List<String> getNext(String word, HashSet<String> dict) {
|
|
|
ArrayList<String> res = new ArrayList<String>();
|
|
|
char[] chs = word.toCharArray();
|
|
|
for (char cur = 'a'; cur <= 'z'; cur++) {
|
|
|
for (int i = 0; i < chs.length; i++) {
|
|
|
if (chs[i] != cur) {
|
|
|
char tmp = chs[i];
|
|
|
chs[i] = cur;
|
|
|
if (dict.contains(String.valueOf(chs))) {
|
|
|
res.add(String.valueOf(chs));
|
|
|
}
|
|
|
chs[i] = tmp;
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
return res;
|
|
|
}
|
|
|
|
|
|
// 生成距离表，从start开始，根据邻居表，宽度优先遍历，对于能够遇到的所有字符串，生成(字符串，距离)这条记录，放入距离表中
|
|
|
public static HashMap<String, Integer> getDistances(String start, HashMap<String, List<String>> nexts) {
|
|
|
HashMap<String, Integer> distances = new HashMap<>();
|
|
|
distances.put(start, 0);
|
|
|
Queue<String> queue = new LinkedList<>();
|
|
|
queue.add(start);
|
|
|
HashSet<String> set = new HashSet<>();
|
|
|
set.add(start);
|
|
|
while (!queue.isEmpty()) {
|
|
|
String cur = queue.poll();
|
|
|
for (String next : nexts.get(cur)) {
|
|
|
if (!set.contains(next)) {
|
|
|
distances.put(next, distances.get(cur) + 1);
|
|
|
queue.add(next);
|
|
|
set.add(next);
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
return distances;
|
|
|
}
|
|
|
|
|
|
// cur 当前来到的字符串 可变
|
|
|
// to 目标，固定参数
|
|
|
// nexts 每一个字符串的邻居表
|
|
|
// cur 到开头距离5 -> 到开头距离是6的支路 fromDistances距离表
|
|
|
// cur 到结尾距离5 -> 到开头距离是4的支路 toDistances距离表
|
|
|
// path : 来到cur之前，深度优先遍历之前的历史是什么
|
|
|
// res : 当遇到cur，把历史，放入res，作为一个结果
|
|
|
public static void getShortestPaths(String cur, String to, HashMap<String, List<String>> nexts,
|
|
|
HashMap<String, Integer> fromDistances, HashMap<String, Integer> toDistances, LinkedList<String> path,
|
|
|
List<List<String>> res) {
|
|
|
path.add(cur);
|
|
|
if (to.equals(cur)) {
|
|
|
res.add(new LinkedList<String>(path));
|
|
|
} else {
|
|
|
for (String next : nexts.get(cur)) {
|
|
|
if (fromDistances.get(next) == fromDistances.get(cur) + 1
|
|
|
&& toDistances.get(next) == toDistances.get(cur) - 1) {
|
|
|
getShortestPaths(next, to, nexts, fromDistances, toDistances, path, res);
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
path.pollLast();
|
|
|
}
|
|
|
|
|
|
}
|
