LeetCode 797. All Paths From Source to Target
原题链接在这里:https://leetcode.com/problems/all-paths-from-source-to-target/
题目:
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.
题解:
Could use DFS to iterate from 0 to n - 1.
DFS state needs graph, current node, end node, current list item and res. It doesn‘t need to return anything, thus void.
Time Complexity: O(V + E). V = graph.length. E is all the edges.
Space: O(E). stack space.
AC Java:
class Solution { public List<List<Integer>> allPathsSourceTarget(int[][] graph) { List<List<Integer>> res = new ArrayList<>(); if(graph == null ||graph.length == 0){ return res; } List<Integer> item = new ArrayList<Integer>(); item.add(0); dfs(graph, 0, graph.length - 1, item, res); return res; } private void dfs(int [][] graph, int cur, int end, List<Integer> item, List<List<Integer>> res){ if(cur == end){ res.add(new ArrayList<Integer>(item)); return; } for(int neigh : graph[cur]){ item.add(neigh); dfs(graph, neigh, end, item, res); item.remove(item.size() - 1); } } }
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