1 files changed, 191 insertions, 0 deletions
diff --git a/Year_1/Programming_2/data_structures/dfs.cc b/Year_1/Programming_2/data_structures/dfs.cc
new file mode 100644
index 0000000..744f153
--- /dev/null
+++ b/Year_1/Programming_2/data_structures/dfs.cc
@@ -0,0 +1,191 @@
+#include<iostream>
+#include<vector>
+#include<queue>
+#define W -1
+#define G 0
+#define B 1
+
+using namespace std;
+
+template<class H>
+class node {
+public:
+    explicit node(H key, node<H>* next) : _key{key}, _next(next) {}
+    const H& key() const { return _key; }
+    H& key() { return _key; }
+    const node<H>*& next() const { return _next; }
+    node<H>*& next() { return _next; }
+private:
+    H _key;
+    node<H>* _next;
+};
+
+template<class H>
+class list {
+public:
+    list() : _head{nullptr} {}
+    ~list() {
+        while(_head) {
+            auto tmp = _head;
+            _head = _head->next();
+            delete tmp;
+        }
+    }
+    list<H>* push(H val) {
+        auto iter = _head;
+        while(iter && iter->next())
+            iter = iter->next();
+
+        if(!iter)
+            _head = new node<H>{val, nullptr};
+        else
+            iter->next() = new node<H>{val, nullptr};
+
+        return this;
+    }
+    void print() {
+        auto iter = _head;
+        while(iter) {
+            cout << iter->key() << ' ';
+            iter = iter->next();
+        }
+    }
+    vector<H> as_vector() {
+        vector<H> v;
+        auto iter = _head;
+        while(iter) {
+            v.push_back(iter->key());
+            iter = iter->next();
+        }
+        return v;
+    }
+    node<H>* search(H val) {
+        auto iter = _head;
+        while(iter && iter->key() != val) {
+            iter = iter->next();
+        }
+
+        return iter;
+    }
+private:
+    node<H>* _head;
+};
+
+template<class H>
+class graph {
+private:
+    int _len, _nodes, _edges;
+    int* _parents;
+    int* _radixes;
+    int* _distances;
+    int* _finishes;
+    int* _colors;
+    int _time;
+    int _current;
+    H** _k; // it works like a dictionary, it saves the keys
+    list<int>** _adj;
+    int _index(H val) {
+        for(int i = 0; i < _nodes; ++i)
+            if(*_k[i] == val) return i;
+
+        return -1;
+    }
+    void _dfsvisit(int u) {
+        _colors[u] = G;
+        _distances[u] = _time++;
+        _radixes[u] = _current;
+        for(auto const& v : _adj[u]->as_vector()) {
+            if(_colors[v] == W) {
+                _parents[v] = u;
+                _dfsvisit(v);
+            }
+        }
+        _colors[u] = B;
+        _finishes[u] = _time++;
+    }
+public:
+    graph(int len) : _len{len}, _nodes{0}, _edges{0} {
+        _k = new H*[len];
+        _adj = new list<int>*[_len];
+        _parents = new int[_len];
+        _radixes = new int[_len];
+        _distances = new int[_len];
+        _finishes = new int[_len];
+        _colors = new int[_len];
+        for(int i = 0; i < _len; ++i) {
+            _k[i] = nullptr;
+            _adj[i] = new list<int>{};
+        }
+    }
+
+    graph<H>* add_node(H k) {
+        if(_nodes == _len) return this;
+        if(_index(k) >= 0) return this; // node is already there
+
+        _k[_nodes++] = new H(k);
+
+        return this;
+    }
+
+
+    void dfs() {
+        _time = 0;
+        for(int i = 0; i < _nodes; ++i) {
+            _colors[i] = W;
+            _parents[i] = -1;
+        }
+
+        for(int i = 0; i < _nodes; ++i) {
+            if(_colors[i] == W) {
+                _current = i;
+                _dfsvisit(i);
+            }
+        }
+        for(int i = 0; i < _nodes; ++i) {
+            cout << *_k[i] << "(" << _distances[i]+1 << ',' << _finishes[i]+1 << ")" << endl;
+        }
+    }
+
+    graph<H>* add_edge(H x, H y) {
+        int i = _index(x);
+        int j = _index(y);
+        if(i < 0 || j < 0) return this;
+
+        if(!_adj[i]->search(j)) {
+            _adj[i]->push(j);
+            _edges++;
+        }
+
+        return this;
+    }
+
+    void print() {
+        for(int i = 0; i < _nodes; ++i) {
+            cout << "(" << i << ", " << *_k[i] << "): ";
+            for(auto const& j : _adj[i]->as_vector())
+                cout << "(" << j << ", " << *_k[j] << "), ";
+            cout << '\n';
+        } 
+    }
+};
+
+
+int main() {
+    graph<char>* g = new graph<char>(6);
+    g->add_node('u')->add_node('v')->add_node('x')->add_node('y');
+    g->add_node('w')->add_node('z');
+    g->add_edge('u', 'v');
+    g->add_edge('u', 'x');
+    g->add_edge('x', 'v');
+    g->add_edge('y', 'x');
+    g->add_edge('v', 'y');
+    g->add_edge('w', 'y');
+    g->add_edge('w', 'z');
+    g->add_edge('z', 'z');
+
+    g->print();
+    g->dfs();
+
+    delete g;
+    return 0;
+}