添加拓扑排序、最小生成树算法

minimum-spanning-tree.cpp

@@ -0,0 +1,114 @@
+class MST
+{
+    /**
+    *   Minumum Spanning Tree
+    *
+    */
+
+private:
+    vector<int> _pre;      // pre-node
+    vector<int> _size;     // size of node
+
+     /*!
+      * @brief       :   finding function of union set
+      * @param [x]   :   node index
+      * @retval      :   parent node
+      */
+    int find(int x)
+    {
+        if (_pre[x] == x)
+            return x;
+        _pre[x] = find(_pre[x]);
+        return _pre[x];
+    }
+public:
+    /*!
+     * @brief               :   prim  minimum spanning tree algorithm
+     * @param [num_nodes]   :   number of nodes
+     * @param [connections] :   inter-node connection distance [start<72><74>end<6E><64>distance]
+     * @retval              :   minimum weighted-sum
+     */
+    int prim(int num_nodes, vector<vector<int>>& connections)
+    {
+        vector<vector<pair<int, int>>> edges(n);
+        for (size_t i = 0; i < connections.size(); i++) {
+            int city_a = connections[i][0], city_b = connections[i][1];
+            int cost = connections[i][2];
+            edges[city_a].push_back(make_pair(city_b, cost));
+            edges[city_b].push_back(make_pair(city_a, cost));
+        }
+        set<int> intree;                        // set of visited node
+        vector<pair<int, int>> out_edges;       // external edge
+        out_edges.push_back(make_pair(0, 0));   // target node
+
+        int ans = 0;
+        
+        // iterate over all outward expanding edges until all nodes are visited
+        while (out_edges.size() != 0 && intree.size() != num_nodes)
+        {
+            // find the edge with minimal weight
+            vector<pair<int, int>>::iterator iter = min_element(out_edges.begin(), out_edges.end(), [&](pair<int, int>& elem1, pair<int, int>elem2)
+                {
+                    return elem1.second < elem2.second;
+
+                });
+            pair<int, int> out_edge = *iter;
+            out_edges.erase(iter);
+
+            // add unvisited node
+            if (intree.find(out_edge.first) == intree.end())
+            {
+                intree.insert(out_edge.first);
+                ans += out_edge.second;
+                for (pair<int, int> edge : edges[out_edge.first])
+                {
+                    out_edges.push_back(make_pair(edge.first, edge.second));
+                }
+            }
+        }
+        
+        if (intree.size() != num_nodes)
+            return -1;      // not exist if two nodes is not connected
+        return ans;
+    }
+
+
+    /*!
+     * @brief               :   Kruskal MST algorithm
+     * @param [num_nodes]   :   Number of nodes
+     * @param [connections] :   Inter-node connection distance [start<72><74>end<6E><64>distance]
+     * @retval              :   Minimum weighted-sum
+     */
+    int kruskal(int numNodes, vector<vector<int>>& connections)
+        _pre.resize(numNodes), _size.resize(numNodes, 1);
+        iota(_pre.begin(), _pre.end(), 0);
+
+        // sort with the distance
+        sort(connections.begin(), connections.end(), [&](vector<int>& elem1, vector<int>& elem2) {
+            return elem1.at(2) < elem2.at(2);
+            });
+
+        int ans = 0;                 // minimum weighted-sum
+        int edge_count = 0;          // number of visited nodes
+        for (size_t i = 0; i < connections.size(); i++) {
+            int x = find(connections[i][0]), y = find(connections[i][1]);
+
+            // Union find set
+            if (x != y) {
+                if (_size[x] > _size[y]) {
+                    swap(x, y);
+                }
+
+                _pre[x] = y;
+                _size[y] += _size[x];
+                ans += connections[i][2];
+                edge_count++;
+                if (edge_count == numNodes - 1) {
+                    return ans;
+                }
+            }
+        }
+
+        return -1;  // not exist if two nodes is not connected
+    }
+};