Time: 8 ms (94.28%), Space: 8.9 MB (85.67%) - LeetHub

Author: JanaSabuj

word-ladder-ii/word-ladder-ii.cpp

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+class Solution {
+public:
+    vector<vector<string>> globalAns;
+    unordered_map<string, int> depth;
+    unordered_map<string, vector<string>> adj;
+
+    int minLenPath(string& beginWord, string& endWord, vector<string>& wordList) {
+        unordered_set<string> dict(wordList.begin(), wordList.end());
+
+        if (dict.find(endWord) == dict.end())
+            return 0;
+
+        queue<string> q;
+        q.push(beginWord);
+        depth[beginWord] = 0;
+
+        while (!q.empty()) {
+            auto x = q.front();
+            q.pop();
+
+            string currWord = x;
+            int currDepth = depth[currWord];
+
+            if (currWord == endWord)
+                return currDepth;
+
+            // check its children
+            for (int i = 0; i < (int)currWord.size(); i++) {
+                char old = currWord[i];
+
+                for (int j = 0; j < 26; j++) {
+                    if ((j + 'a') == old) continue;
+                    currWord[i] = (j + 'a');
+                    
+                    if(dict.find(currWord) == dict.end()) continue;// only if valid word
+                    
+                    if (depth.find(currWord) == depth.end()) {                        
+                        depth[currWord] = currDepth + 1;
+                        adj[x].push_back(currWord);
+                        q.push(currWord);
+                    } else {
+                        if (depth[currWord] == currDepth + 1) {
+                            adj[x].push_back(currWord);
+                        }
+                    }
+                }
+
+                currWord[i] = old;
+            }
+        }
+
+        return 0;
+    }
+
+    void dfs(string currWord, string& endWord, int k, vector<string>& path) {
+        path.push_back(currWord);
+
+        if (k == 0) {
+            if (currWord == endWord) {
+                globalAns.push_back(path);             
+            }
+            
+            path.pop_back();
+            return;
+        }
+
+        for (auto u : adj[currWord])
+            dfs(u, endWord, k - 1, path);
+
+        path.pop_back();
+    }
+
+    vector<vector<string>> findLadders(string beginWord, string endWord,
+    vector<string>& wordList) {
+        // 1 - find min length of path k
+        int k = minLenPath(beginWord, endWord, wordList);
+
+        // 2 - traverse all paths of length k and print all paths ending with endWord
+        if (k == 0)
+            return {};
+        
+        cout << k << endl;
+        vector<string> path;
+        dfs(beginWord, endWord, k, path);
+
+        return globalAns;
+    }
+};