1+ package javacode .solutions ;
2+ 3+ import java .util .*;
4+ 5+ // [Problem] https://leetcode.com/problems/find-if-path-exists-in-graph
6+ class FindIfPathExistsInGraph {
7+ // BFS
8+ // O(v + e) time, O(v + e) space
9+ public boolean validPathBfs (int n , int [][] edges , int source , int destination ) {
10+ HashSet <Integer >[] graph = new HashSet [n ];
11+ for (int i = 0 ; i < n ; i ++) {
12+ graph [i ] = new HashSet <>();
13+ }
14+ for (int [] edge : edges ) {
15+ graph [edge [0 ]].add (edge [1 ]);
16+ graph [edge [1 ]].add (edge [0 ]);
17+ }
18+ boolean [] visited = new boolean [n ];
19+ Queue <Integer > nodesToVisit = new ArrayDeque <>();
20+ nodesToVisit .add (source );
21+ visited [source ] = true ;
22+ while (!nodesToVisit .isEmpty ()) {
23+ int nextNodes = nodesToVisit .size ();
24+ for (int i = 0 ; i < nextNodes ; i ++) {
25+ int node = nodesToVisit .poll ();
26+ if (node == destination ) {
27+ return true ;
28+ }
29+ Set <Integer > connectedNodes = graph [node ];
30+ for (int connectedNode : connectedNodes ) {
31+ if (!visited [connectedNode ]) {
32+ nodesToVisit .add (connectedNode );
33+ visited [node ] = true ;
34+ }
35+ }
36+ }
37+ }
38+ return false ;
39+ }
40+ 41+ // DFS
42+ // O(v + e) time, O(v + e) space
43+ public boolean validPath (int n , int [][] edges , int source , int destination ) {
44+ HashSet <Integer >[] graph = new HashSet [n ];
45+ for (int i = 0 ; i < n ; i ++) {
46+ graph [i ] = new HashSet <>();
47+ }
48+ for (int [] edge : edges ) {
49+ graph [edge [0 ]].add (edge [1 ]);
50+ graph [edge [1 ]].add (edge [0 ]);
51+ }
52+ return dfs (graph , new boolean [n ], source , destination );
53+ }
54+ 55+ private boolean dfs (HashSet <Integer >[] graph , boolean [] visited , int source , int destination ) {
56+ if (source == destination ) {
57+ return true ;
58+ }
59+ visited [source ] = true ;
60+ Set <Integer > connectedNodes = graph [source ];
61+ for (int connectedNode : connectedNodes ) {
62+ if (!visited [connectedNode ] && dfs (graph , visited , connectedNode , destination )) {
63+ return true ;
64+ }
65+ }
66+ return false ;
67+ }
68+ 69+ // Test
70+ public static void main (String [] args ) {
71+ FindIfPathExistsInGraph solution = new FindIfPathExistsInGraph ();
72+ 73+ int [][] edges1 = {{0 , 1 }, {1 , 2 }, {2 , 0 }};
74+ boolean expectedOutput1 = true ;
75+ boolean actualOutput1 = solution .validPath (3 , edges1 , 0 , 2 );
76+ System .out .println ("Test 1 passed? " + (expectedOutput1 == actualOutput1 ));
77+ 78+ int [][] edges2 = {{0 , 1 }, {0 , 2 }, {3 , 5 }, {5 , 4 }, {4 , 3 }};
79+ boolean expectedOutput2 = false ;
80+ boolean actualOutput2 = solution .validPath (6 , edges2 , 0 , 5 );
81+ System .out .println ("Test 2 passed? " + (expectedOutput2 == actualOutput2 ));
82+ }
83+ }
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