LeetCode-in-Java

797. All Paths From Source to Target

Medium

Given a directed acyclic graph (DAG) of n nodes labeled from 0 to n - 1, find all possible paths from node 0 to node n - 1 and return them in any order.

The graph is given as follows: graph[i] is a list of all nodes you can visit from node i (i.e., there is a directed edge from node i to node graph[i][j]).

Example 1:

Input: graph = [[1,2],[3],[3],[]]

Output: [[0,1,3],[0,2,3]]

Explanation: There are two paths: 0 -> 1 -> 3 and 0 -> 2 -> 3.

Example 2:

Input: graph = [[4,3,1],[3,2,4],[3],[4],[]]

Output: [[0,4],[0,3,4],[0,1,3,4],[0,1,2,3,4],[0,1,4]]

Constraints:

• n == graph.length
• 2 <= n <= 15
• 0 <= graph[i][j] < n
• graph[i][j] != i (i.e., there will be no self-loops).
• All the elements of graph[i] are unique.
• The input graph is guaranteed to be a DAG.

Solution

import java.util.ArrayList;
import java.util.List;

public class Solution {
    private List<List<Integer>> res;

    public List<List<Integer>> allPathsSourceTarget(int[][] graph) {
        res = new ArrayList<>();
        List<Integer> temp = new ArrayList<>();
        temp.add(0);
        // perform DFS
        solve(graph, temp, 0);
        return res;
    }

    private void solve(int[][] graph, List<Integer> temp, int lastNode) {
        if (lastNode == graph.length - 1) {
            res.add(new ArrayList<>(temp));
        }
        for (int link : graph[lastNode]) {
            temp.add(link);
            solve(graph, temp, link);
            temp.remove(temp.size() - 1);
        }
    }
}

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