4.2 Given a directed graph, design an algorithm to find out whether there is a route between two nodes.
LeetCode和CareerCup中关于图的题都不是很多，LeetCode中只有三道，分别是Clone Graph 无向图的复制，Course Schedule 课程清单 和 Course Schedule II 课程清单之二。目前看来CareerCup中有关图的题在第四章中仅此一道，这是一道关于有向图的题，书中是用java来做的，我们用c++来做时要定义图和节点，这里参考了之前那道Clone Graph 无向图的复制中关于无向图的定义，并且在里面加入了一个枚举类变量state，来帮助我们遍历。这种找两点之间路径的题就是遍历的问题，可以用BFS或DFS来解，先来看BFS的解法，如下所示：
//Definition for directed graph. enum State { Unvisited, Visited, Visiting }; struct DirectedGraphNode { int label; State state; vector<DirectedGraphNode *> neighbors; DirectedGraphNode(int x) : label(x) {}; }; struct DirectedGraph { vector<DirectedGraphNode*> nodes; }; class Solution { public: bool search(DirectedGraph *g, DirectedGraphNode *start, DirectedGraphNode *end) { queue<DirectedGraphNode*> q; for (auto a : g->nodes) a->state = Unvisited; start->state = Visiting; q.push(start); while (!q.empty()) { DirectedGraphNode *node = q.front(); q.pop(); for (auto a : node->neighbors) { if (a->state == Unvisited) { if (a == end) return true; else { a->state = Visiting; q.push(a); } } } node->state = Visited; } return false; } };
本文转自博客园Grandyang的博客，原文链接：有向图中两点的路径[CareerCup] 4.2 Route between Two Nodes in Directed Graph ，如需转载请自行联系原博主。
