Merge pull request #144 from tanmay-dev-001/main

Created Alien Dictionary

Author: admirerr

CPP/graph/Alien Dictionary

@@ -0,0 +1,86 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+/*
+    Alien Dictionary Problem
+    ------------------------
+    Given a sorted dictionary of an alien language (lexicographically sorted),
+    find the order of characters in the alien alphabet.
+
+    Approach:
+    - Build a directed graph where an edge u → v means 'u' comes before 'v'.
+    - Perform topological sort (Kahn's Algorithm) to get the character order.
+*/
+
+class Solution {
+public:
+    string findOrder(vector<string>& dict, int K) {
+        // Step 1: Build adjacency list for K characters
+        vector<int> adj[K];
+
+        // Compare adjacent words to find ordering
+        for (int i = 0; i < dict.size() - 1; i++) {
+            string word1 = dict[i];
+            string word2 = dict[i + 1];
+            int len = min(word1.size(), word2.size());
+
+            for (int j = 0; j < len; j++) {
+                if (word1[j] != word2[j]) {
+                    adj[word1[j] - 'a'].push_back(word2[j] - 'a');
+                    break; // Only first differing character matters
+                }
+            }
+        }
+
+        // Step 2: Perform Topological Sort (Kahn's Algorithm)
+        vector<int> indegree(K, 0);
+        for (int i = 0; i < K; i++) {
+            for (auto it : adj[i])
+                indegree[it]++;
+        }
+
+        queue<int> q;
+        for (int i = 0; i < K; i++) {
+            if (indegree[i] == 0)
+                q.push(i);
+        }
+
+        string order;
+        while (!q.empty()) {
+            int node = q.front();
+            q.pop();
+
+            order += (node + 'a');
+
+            for (auto neigh : adj[node]) {
+                indegree[neigh]--;
+                if (indegree[neigh] == 0)
+                    q.push(neigh);
+            }
+        }
+
+        // Step 3: Return result
+        return order;
+    }
+};
+
+int main() {
+    /*
+        Example:
+        Dictionary = {"baa", "abcd", "abca", "cab", "cad"}
+        K = 4  (characters: a, b, c, d)
+
+        Possible order: b -> d -> a -> c
+        Output: "bdac" (or another valid topological ordering)
+    */
+
+    vector<string> dict = {"baa", "abcd", "abca", "cab", "cad"};
+    int K = 4;
+
+    Solution sol;
+    string result = sol.findOrder(dict, K);
+
+    cout << "Alien Dictionary Order: " << result << endl;
+
+    return 0;
+}