[LintCode] 拓扑排序

BFS:

 1 /**
 2  * Definition for Directed graph.
 3  * struct DirectedGraphNode {
 4  *     int label;
 5  *     vector<DirectedGraphNode *> neighbors;
 6  *     DirectedGraphNode(int x) : label(x) {};
 7  * };
 8  */
 9 class Solution {
10 public:
11     /**
12      * @param graph: A list of Directed graph node
13      * @return: Any topological order for the given graph.
14      */
15     vector<DirectedGraphNode*> topSort(vector<DirectedGraphNode*> graph) {
16         // write your code here
17         vector<DirectedGraphNode*> topo;
18         unordered_map<DirectedGraphNode*, int> degrees = compute_indegree(graph);
19         queue<DirectedGraphNode*> zeros;
20         for (auto itr = degrees.begin(); itr != degrees.end(); itr++)
21             if ((*itr).second == 0)
22                 zeros.push((*itr).first);
23         while (!zeros.empty()) {
24             DirectedGraphNode* zero = zeros.front();
25             zeros.pop();
26             topo.push_back(zero);
27             for (DirectedGraphNode* neigh : zero -> neighbors)
28                 if (--degrees[neigh] == 0)
29                     zeros.push(neigh);
30         }
31         return topo;
32     }
33 private:
34     unordered_map<DirectedGraphNode*, int> compute_indegree(vector<DirectedGraphNode*>& graph) {
35         unordered_map<DirectedGraphNode*, int> degrees;
36         for (DirectedGraphNode* node : graph) {
37             if (degrees.find(node) == degrees.end())
38                 degrees[node] = 0;
39             for (DirectedGraphNode* neigh : node -> neighbors)
40                 degrees[neigh]++;
41         }
42         return degrees;
43     }
44 };

DFS:

 1 /**
 2  * Definition for Directed graph.
 3  * struct DirectedGraphNode {
 4  *     int label;
 5  *     vector<DirectedGraphNode *> neighbors;
 6  *     DirectedGraphNode(int x) : label(x) {};
 7  * };
 8  */
 9 class Solution {
10 public:
11     /**
12      * @param graph: A list of Directed graph node
13      * @return: Any topological order for the given graph.
14      */
15     vector<DirectedGraphNode*> topSort(vector<DirectedGraphNode*> graph) {
16         // write your code here
17         vector<DirectedGraphNode*> topo;
18         unordered_set<DirectedGraphNode*> visited;
19         for (DirectedGraphNode* node : graph)
20             if (visited.find(node) == visited.end())
21                 dfs(graph, node, visited, topo);
22         reverse(topo.begin(), topo.end());
23         return topo;
24     }
25 private:
26     void dfs(vector<DirectedGraphNode*>& graph, DirectedGraphNode* node,
27              unordered_set<DirectedGraphNode*>& visited,
28              vector<DirectedGraphNode*>& topo) {
29         visited.insert(node);
30         for (DirectedGraphNode* neigh : node -> neighbors)
31             if (visited.find(neigh) == visited.end())
32                 dfs(graph, neigh, visited, topo);
33         topo.push_back(node);
34     }
35 };