leetcode 797. All Paths From Source to Target

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.

思路：建树，然后深度优先遍历一遍就行了。

class Solution {
public:
    vector<int> edge[20];
    vector<vector<int> > ans;
    int n;
    void dfs(int u, vector<int>& t) {
        t.push_back(u);
        if (u == n-1) {
            ans.push_back(t);
            return ;
        }
        for (int i = 0; i < edge[u].size(); ++i) {
            dfs(edge[u][i], t);
            t.pop_back();
        }
    }
    vector<vector<int>> allPathsSourceTarget(vector<vector<int>>& graph) {
        n = graph.size();
        for (int i = 0; i < graph.size(); ++i) {
            for (int j = 0; j < graph[i].size(); ++j) {
                edge[i].push_back(graph[i][j]);
            }
        }
        vector<int> t;
        dfs(0, t);
        return ans;
    }
};