Added World Ladder problem I and II

Word Ladder/Word_Ladder_I.cpp

@@ -0,0 +1,89 @@
+// Word Ladder I
+// Problem statement:
+/*
+    Given two distinct words startWord and targetWord, and a list denoting wordList of unique words of equal lengths. Find the length of the shortest transformation sequence from startWord to targetWord.
+    Keep the following conditions in mind:
+
+    -> A word can only consist of lowercase characters.
+    -> Only one letter can be changed in each transformation.
+    -> Each transformed word must exist in the wordList including the targetWord.
+    -> startWord may or may not be part of the wordList.
+
+    If no possible way to transform sequence from startWord to targetWord return 0.
+*/
+// Test Case:
+
+/*
+Input:
+wordList = {"des","der","dfr","dgt","dfs"}
+startWord = "der", targetWord= "dfs",
+Output:
+3
+Explanation:
+The length of the smallest transformation
+sequence from "der" to "dfs" is 3
+i,e "der" -> "dfr" -> "dfs".
+*/
+
+#include<bits/stdc++.h>
+using namespace std;
+
+class Solution {
+public:
+    // TC -> O(N) [wordList length] * O(word length) * O(26) * O(logN) [set]
+    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
+        queue<pair<string, int>> q;
+        // converting vector of wordList to set of wordList 
+        // because it is easier to search as word in set then in a vector
+        unordered_set<string> s(wordList.begin(), wordList.end());
+
+        q.push({beginWord, 1}); // holds the beginning word and initial step as 1
+
+        // we are deleting the already traversed word because forming the same word again
+        // has no point, we want to form the new words and not loop witing the same set of words
+        s.erase(beginWord);
+
+        while(!q.empty()){
+            string word = q.front().first;
+            int steps = q.front().second;
+            q.pop();
+            if(word == endWord) return steps;
+
+            // traverse through all the characters of the word
+            for(int i = 0; i < word.size(); i++){
+
+                string original = word;
+
+                // change each character to some different letters from a-z
+                for(char ch = 'a'; ch <= 'z'; ch++)
+                {
+                    word[i] = ch;
+
+                    // if any of the word exist in wordList we will take that word
+                    if(s.count(word)){
+                        s.erase(word);
+                        q.push({word, steps+1});
+                    }
+                }
+                word = original; // undo the changes made.
+            }
+        }
+        return 0;
+    }
+};
+int main(){
+	int tc;
+	cin >> tc;
+	while(tc--){
+		int n;
+		cin >> n;
+		vector<string>wordList(n);
+		for(int i = 0; i < n; i++)cin >> wordList[i];
+		string startWord, targetWord;
+		cin >> startWord >> targetWord;
+		Solution obj;
+		int ans = obj.ladderLength(startWord, targetWord, wordList);
+		cout << ans << "\n";
+	}
+	return 0;
+}

Word Ladder/Word_Ladder_II.cpp

@@ -0,0 +1,126 @@
+// Word Ladder II 
+// Problem statement:
+/*
+Given two distinct words startWord and targetWord, and a list denoting wordList of unique words of equal lengths. Find all shortest transformation sequence(s) from startWord to targetWord. You can return them in any order possible.
+Keep the following conditions in mind:
+
+-> A word can only consist of lowercase characters.
+-> Only one letter can be changed in each transformation.
+-> Each transformed word must exist in the wordList including the targetWord.
+-> startWord may or may not be part of the wordList.
+-> Return an empty list if there is no such transformation sequence.
+*/
+
+// Test Case:
+/*
+Input:
+startWord = "der", targetWord = "dfs",
+wordList = {"des","der","dfr","dgt","dfs"}
+Output:
+der dfr dfs
+der des dfs
+Explanation:
+The length of the smallest transformation is 3.
+And the following are the only two ways to get
+to targetWord:-
+"der" -> "des" -> "dfs".
+"der" -> "dfr" -> "dfs".
+*/
+
+#include<bits/stdc++.h>
+using namespace std;
+
+class Solution {
+public:
+    vector<vector<string>> findSequences(string beginWord, string endWord, vector<string>& wordList) {
+        unordered_set<string> st(wordList.begin(), wordList.end());
+        queue<vector<string>> q;
+        q.push({beginWord});
+        // stores used words from wordList of previous level
+        vector<string> usedOnLevel;
+        usedOnLevel.push_back(beginWord);
+        int level = 0;
+        vector<vector<string>> ans;
+        while(!q.empty())
+        {
+            // stores the current level word sequence
+            vector<string> v = q.front();
+            q.pop();
+
+            // erase all the words that has been
+            // used in the previous level to transform
+            while(v.size() > level)
+            {
+                level++;
+                for(auto it: usedOnLevel)
+                    st.erase(it);
+            }
+
+            string word = v.back();
+            if(word == endWord)
+                ans.push_back(v);
+            for(int i = 0; i < word.size(); i++)
+            {
+                char original = word[i];
+                for(char ch = 'a'; ch <= 'z'; ch++){
+                    word[i] = ch;
+                    if(st.count(word))
+                    {
+                        // if transformed word exists in wordList
+                        // add it to the sequence
+                        v.push_back(word);
+                        q.push(v);
+
+                        // mark the word as visited on that level
+                        usedOnLevel.push_back(word);
+                        // undo the changes made in word sequenece
+                        // so that it can be changed to some other word
+                        // on the same level
+                        v.pop_back();
+                    }
+                }
+                word[i] = original; // undo the character changes
+            }
+        }
+        return ans;
+    }
+};
+bool comp(vector<string> a, vector<string> b)
+{
+    string x = "", y = "";
+    for(string i: a)
+        x += i;
+    for(string i: b)
+        y += i;
+
+    return x<y;
+}
+int main(){
+	int tc;
+	cin >> tc;
+	while(tc--){
+		int n;
+		cin >> n;
+		vector<string>wordList(n);
+		for(int i = 0; i < n; i++)cin >> wordList[i];
+		string startWord, targetWord;
+		cin >> startWord >> targetWord;
+		Solution obj;
+		vector<vector<string>> ans = obj.findSequences(startWord, targetWord, wordList);
+		if(ans.size()==0)
+		    cout<<-1<<endl;
+		else
+		{
+		    sort(ans.begin(), ans.end(), comp);
+            for(int i=0; i<ans.size(); i++)
+            {
+                for(int j=0; j<ans[i].size(); j++)
+                {
+                    cout<<ans[i][j]<<" ";
+                }
+                cout<<endl;
+            }
+		}
+	}
+	return 0;
+}