LeetCode in Kotlin

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

class Solution {
    private var res: MutableList<List<Int>>? = null
    fun allPathsSourceTarget(graph: Array<IntArray>): List<List<Int>> {
        res = ArrayList()
        val temp: MutableList<Int> = ArrayList()
        temp.add(0)
        // perform DFS
        solve(graph, temp, 0)
        return res as ArrayList<List<Int>>
    }

    private fun solve(graph: Array<IntArray>, temp: MutableList<Int>, lastNode: Int) {
        if (lastNode == graph.size - 1) {
            res!!.add(ArrayList(temp))
        }
        for (link in graph[lastNode]) {
            temp.add(link)
            solve(graph, temp, link)
            temp.removeAt(temp.size - 1)
        }
    }
}

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