126. Word Ladder II (java)

Author: bluesword12350

solution/0126.Word Ladder II/Solution.java

@@ -0,0 +1,64 @@
+class Solution {
+    private boolean isConnected = false;
+    private Map<String, List<String>> hs;
+    public List<List<String>> findLadders(String beginWord, String endWord, List<String> wordList) {
+        hs = new HashMap<>(16);
+        List<List<String>> result = new ArrayList<>();
+        if(!wordList.contains(endWord))
+            return result;
+        HashSet<String> dict = new HashSet<>(wordList);
+        Set<String> fwd = new HashSet<>();
+        fwd.add(beginWord);
+        Set<String> bwd = new HashSet<>();
+        bwd.add(endWord);
+        bfs(fwd, bwd, dict, false);
+        if(!isConnected) return result;
+        List<String> temp = new ArrayList<>();
+        temp.add(beginWord);
+        dfs(result, temp, beginWord, endWord);
+        return result;
+    }
+    private void bfs(Set<String> forward, Set<String> backward, Set<String> dict, boolean swap){
+        if(forward.isEmpty() || backward.isEmpty()) return;
+        if(forward.size() > backward.size()){
+            bfs(backward, forward, dict, !swap);
+            return;
+        }
+        dict.removeAll(forward);
+        dict.removeAll(backward);
+        Set<String> set3 = new HashSet<>();
+        for(String str : forward)
+            for (int i = 0; i < str.length(); i++) {
+                char[] ary = str.toCharArray();
+                for (char j = 'a'; j <= 'z'; j++) {
+                    ary[i] = j;
+                    String temp = new String(ary);
+                    if (!backward.contains(temp) && !dict.contains(temp)) continue;
+                    String key = !swap ? str : temp;
+                    String val = !swap ? temp : str;
+                    if (!hs.containsKey(key)) hs.put(key, new ArrayList<>());
+                    if (backward.contains(temp)) {
+                        hs.get(key).add(val);
+                        isConnected = true;
+                    }
+                    if (!isConnected && dict.contains(temp)) {
+                        hs.get(key).add(val);
+                        set3.add(temp);
+                    }
+                }
+            }
+        if(!isConnected) bfs(set3, backward, dict, swap);
+    }
+    private void dfs(List<List<String>> result, List<String> temp, String start, String end){
+        if(start.equals(end)){
+            result.add(new ArrayList<>(temp));
+            return;
+        }
+        if(!hs.containsKey(start)) return;
+        for(String s : hs.get(start)){
+            temp.add(s);
+            dfs(result, temp, s, end);
+            temp.remove(temp.size()-1);
+        }
+    }
+}