From 53684a0c6b39c4e2a3ae2d40ecbcad2dac63183b Mon Sep 17 00:00:00 2001
From: Argha Sen <iamslowdeath@gmail.com>
Date: Sun, 28 Oct 2018 13:20:26 +0530
Subject: [PATCH] find alphabets from alien dictionary

---
 alphabets.cpp | 162 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 162 insertions(+)
 create mode 100644 alphabets.cpp

diff --git a/alphabets.cpp b/alphabets.cpp
new file mode 100644
index 000000000..3b843599d
--- /dev/null
+++ b/alphabets.cpp
@@ -0,0 +1,162 @@
+#include <iostream>
+#include <string>
+#include <set>
+#include <vector>
+#include <stack>
+#include <unordered_map>
+#include <iterator>
+#include <algorithm>
+
+using namespace std;
+
+using Vertex = char;
+using Vertices = set<Vertex>;
+using AdjList = unordered_map<Vertex, Vertices>;
+
+class Graph
+{
+  private:
+    int numVertices;
+    AdjList adjList;
+    Vertices vertices;
+
+  public:
+    Graph(Vertices vertices);
+    int getNumVertices() const;
+    const Vertices &getVertices() const;
+    void addEdge(Vertex from, Vertex to);
+    void printAdjList();
+    const Vertices &getNeighbours(Vertex vertex) const;
+};
+
+Graph::Graph(Vertices vertices)
+    : vertices(vertices)
+{
+    numVertices = vertices.size();
+    for (auto vertex : vertices)
+    {
+        adjList.insert(make_pair(vertex, set<Vertex>()));
+    }
+}
+
+int Graph::getNumVertices() const
+{
+    return numVertices;
+}
+
+const Vertices &Graph::getVertices() const
+{
+    return vertices;
+}
+void Graph::addEdge(Vertex from, Vertex to)
+{
+    adjList[from].insert(to);
+}
+
+void Graph::printAdjList()
+{
+    cout << "AdjList:" << endl;
+    for (auto i : adjList)
+    {
+        cout << i.first << " -> [ ";
+        for (auto j : i.second)
+            cout << j << " ";
+        cout << " ]" << endl;
+    }
+}
+
+const Vertices &Graph::getNeighbours(Vertex vertex) const
+{
+    auto res = adjList.find(vertex);
+    return res->second;
+}
+
+void visitor(const Graph &graph, Vertex vertex, unordered_map<Vertex, bool> &visited, stack<Vertex> &s)
+{
+    visited[vertex] = true;
+    auto neighbours = graph.getNeighbours(vertex);
+
+    for (auto neighbour : neighbours)
+    {
+        auto visitItr = visited.find(neighbour);
+        if (visitItr == visited.end() || visitItr->second == false)
+            visitor(graph, neighbour, visited, s);
+    }
+    s.push(vertex);
+}
+
+void topologicalSort(const Graph &graph)
+{
+    stack<char> s;
+    int numVertices = graph.getNumVertices();
+    auto vertices = graph.getVertices();
+    unordered_map<char, bool> visited;
+    for (auto vertex : vertices)
+    {
+        auto visitItr = visited.find(vertex);
+        if (visitItr == visited.end() || visitItr->second == false)
+            visitor(graph, vertex, visited, s);
+    }
+    cout << "Sort Order:" << endl;
+    while (s.empty() == false)
+    {
+        cout << s.top() << " ";
+        s.pop();
+    }
+}
+
+set<char> getAlphabets(vector<string> dict)
+{
+    set<char> alphabets;
+    for (auto &word : dict)
+    {
+        for (int i = 0; i < word.size(); i++)
+        {
+            alphabets.insert(word[i]);
+        }
+    }
+    return alphabets;
+}
+void createGraph(Graph &g, vector<string> dict)
+{
+    string w1, w2;
+    int len;
+    for (int i = 0; i < dict.size() - 1; i++)
+    {
+        w1 = dict[i];
+        w2 = dict[i + 1];
+        len = min(w1.size(), w2.size());
+        for (int j = 0; j < len; j++)
+        {
+            if (w1[j] != w2[j])
+            {
+                g.addEdge(w1[j], w2[j]);
+                break;
+            }
+        }
+    }
+}
+
+int main()
+{
+#ifndef ONLINE_JUDGE
+    freopen("input.txt", "r", stdin);   // redirects standard input
+    freopen("output.txt", "w", stdout); // redirects standard output
+#endif
+    vector<string> dict;
+    string a;
+    while (cin >> a)
+        dict.push_back(a);
+
+    Vertices alphabets = getAlphabets(dict);
+
+    cout << "Alphabets: ";
+    copy(alphabets.begin(), alphabets.end(), ostream_iterator<char>(cout, " "));
+    cout << endl;
+
+    Graph g(alphabets);
+    createGraph(g, dict);
+
+    g.printAdjList();
+    topologicalSort(g);
+}
\ No newline at end of file