797. All Paths From Source to Target

题目描述：

Given a directed, acyclic graph of N nodes.  Find all possible paths from node 0 to node N-1, and return them in any order.

The graph is given as follows:  the nodes are 0, 1, ..., graph.length - 1.  graph[i] is a list of all nodes j for which the edge (i, j) exists.

Example:
Input: [[1,2], [3], [3], []] 
Output: [[0,1,3],[0,2,3]] 
Explanation: The graph looks like this:
0--->1
|    |
v    v
2--->3
There are two paths: 0 -> 1 -> 3 and 0 -> 2 -> 3.

Note:

• The number of nodes in the graph will be in the range [2, 15].
• You can print different paths in any order, but you should keep the order of nodes inside one path.

解题思路：

使用DFS方法或者回溯法，这里使用的是DFS算法。

代码：

class Solution {
public:
    vector<vector<int>> allPathsSourceTarget(vector<vector<int>>& graph) {
        vector<vector<int> >paths;
        vector<int> path;
        dfs(graph, paths, path, 0);
        return paths;
    }
    void dfs(vector<vector<int> >& graph, vector<vector<int> >& paths, vector<int> path, int now) {
        path.push_back(now);
        if (now == graph.size() - 1) {
            paths.push_back(path);
            return;
        }
        for (auto next : graph[now]) {
            dfs(graph, paths, path, next);
        }
    }
};