797. All Paths From Source to Target

[sophuu]

Approach

https://leetcode.com/problems/all-paths-from-source-to-target/description/

DFS through the DAG
Since the size of the input node is 2 <= n <= 15, the approach does not need to be super efficient

1. Start from the first node and traverse through the directed edges by calling dfs iteratively
2. Have the path saved as the parameter to the dfs function
3. When the traversal reaches the end node (n), append the path to the result and end traversing

class Solution:
    def allPathsSourceTarget(self, graph: List[List[int]]) -> List[List[int]]:
        
        def dfs(path):
            if path[-1] == len(graph) - 1:
                res.append(path)
                return
            
            for v in graph[path[-1]]:
                dfs(path + [v])

        res = []
        dfs([0])
        return res

n: number of edges

• Time Complexity: O(n) - O(n^2) depending on the shape of the DAG
• Space Complexity: O(n) as result array

https://leetcode.com/problems/all-paths-from-source-to-target/solutions/986429/python-iterative-dfs-with-detailed-time-complexity-visuals/?orderBy=most_votes