ITint5 046_复制有向图

https://github.com/AnnieKim/ITint5/blob/master/046_%E5%A4%8D%E5%88%B6%E6%9C%89%E5%90%91%E5%9B%BE.cpp
 复制一个有向图。输入是有向图中的一个结点指针，返回复制的图中对应的结点指针。
 Solution: 我在facebook电面时也遇到过这个题目，deep copy一个graph。
*/

/*
有向图中结点的定义为：
struct GraphNode {
    int data;
    vector<GraphNode*> neighbors;
    GraphNode(int data) : data(data) {}
};
*/

/*
 方案 1：DFS。
*/
typedef unordered_map<GraphNode *, GraphNode *> MAP;

GraphNode *cloneGraphRe(GraphNode *node, MAP &exist) {
    if (!node) return NULL;
    if (exist.find(node) != exist.end())
        return exist[node];
    GraphNode *newNode = new GraphNode(node->data);
    exist[node] = newNode;
    for (int i = 0; i < node->neighbors.size(); ++i)
        newNode->neighbors.push_back(cloneGraphRe(node->neighbors[i], exist));
    return newNode;
}

GraphNode *cloneGraph(GraphNode *node) {
    MAP exist;
    return cloneGraphRe(node, exist);
}

/*
 方案 2：BFS。
*/
typedef unordered_map<GraphNode *, GraphNode *> MAP;

GraphNode *cloneGraph(GraphNode *node) {
    if (!node) return NULL;
    MAP exist;
    exist[node] = new GraphNode(node->data);
    queue<GraphNode *> q;
    q.push(node);
    while (!q.empty())
    {
        GraphNode *orig = q.front();
        GraphNode *newNode = exist[orig];
        q.pop();
        for (int i = 0; i < orig->neighbors.size(); ++i)
        {
            if (exist.find(orig->neighbors[i]) != exist.end()) {
                newNode->neighbors.push_back(exist[orig->neighbors[i]]);
                continue;
            }
            GraphNode *newNeighbor = new GraphNode(orig->neighbors[i]->data);
            newNode->neighbors.push_back(newNeighbor);
            exist[orig->neighbors[i]] = newNeighbor;
            q.push(orig->neighbors[i]);
        }
    }
    return exist[node];
}
https://github.com/ralphite/ITint5-Answers-Java/blob/master/%E5%A4%8D%E5%88%B6%E6%9C%89%E5%90%91%E5%9B%BE.java
    public GraphNode cloneGraph(GraphNode node) {
        if(node==null) return null;
        //dfs and add cloned node to it's neighbors
        HashSet<GraphNode> set = new HashSet<GraphNode>();
        dfs(node, set);
        //dfs again to setup the cloned nodes neighbors
        set.clear();
        dfs2(node, set);
       
        GraphNode newNode = node.neighbors.get(node.neighbors.size()-1);
       
        //dfs3 to remove the cloned node from the neighbors list
        //optional if we can change node's structure
        set.clear();
        dfs3(node, set);
       
        return newNode;
    }
    private static void dfs(GraphNode node, HashSet<GraphNode> set) {
        if(node==null) return;
        if(set.contains(node)) return;
        set.add(node);
        for(GraphNode n : node.neighbors) {
            dfs(n, set);
        }
        node.neighbors.add(new GraphNode(node.data));
    }
    private static void dfs2(GraphNode node, HashSet<GraphNode> set) {
        if(node==null) return;
        if(set.contains(node)) return;
        set.add(node);
        GraphNode newNode = node.neighbors.get(node.neighbors.size()-1);
        for(int i = 0; i < node.neighbors.size()-1; i++) {
            GraphNode n = node.neighbors.get(i);
            newNode.neighbors.add(n.neighbors.get(n.neighbors.size()-1));
            dfs2(n, set);
        }
    }
    private static void dfs3(GraphNode node, HashSet<GraphNode> set) {
        if(node==null) return;
        if(set.contains(node)) return;
        set.add(node);
        node.neighbors.remove(node.neighbors.size()-1);
        for(int i = 0; i < node.neighbors.size()-1; i++) {
            GraphNode n = node.neighbors.get(i);
            dfs3(n, set);
        }
    }