solves find path if exists in graph

Author: anishLearnsToCode

README.md

@@ -469,10 +469,10 @@
 | 1941 | [Check if All Characters Have Equal Number of Occurrences](https://leetcode.com/problems/check-if-all-characters-have-equal-number-of-occurrences)        |                                                [![Java](assets/java.png)](src/CheckIfAllCharactersHaveEqualNumberOfOccurrences.java)                                                 |                                                                                                                                   |
 | 1945 | [Sum of Digits of String After Convert](https://leetcode.com/problems/sum-of-digits-of-string-after-convert)                                              |                                                         [![Java](assets/java.png)](src/SumOfDigitsOfStringAfterConvert.java)                                                         |                                                                                                                                   |
 | 1952 | [Three Divisors](https://leetcode.com/problems/three-divisors)                                                                                            |                                                                  [![Java](assets/java.png)](src/ThreeDivisors.java)                                                                  |                                                                                                                                   |
-| 1957 | [Delete Characters to Make Fancy String](https://leetcode.com/problems/delete-characters-to-make-fancy-string)                                            |                                                          [![Java](assets/java.png)](src/CheckIfStringIsAPrefixOfArray.java)                                                          |                                                                                                                                   |
-| 1961 | [Check If String Is a Prefix of Array](https://leetcode.com/problems/check-if-string-is-a-prefix-of-array)                                                |                                                   [![Java](assets/java.png)](src/NumberOfStringsThatAppearAsSubstringsInWord.java)                                                   |                                                                                                                                   |
-| 1967 | [Number of Strings That Appear as Substrings in Word](https://leetcode.com/problems/number-of-strings-that-appear-as-substrings-in-word)                  |                                                                                                                                                                                      |                                                                                                                                   |
-| 1971 | [Find if Path Exists in Graph](https://leetcode.com/problems/find-if-path-exists-in-graph)                                                                |                                                                                                                                                                                      |                                                                                                                                   |
+| 1957 | [Delete Characters to Make Fancy String](https://leetcode.com/problems/delete-characters-to-make-fancy-string)                                            |                                                        [![Java](assets/java.png)](src/DeleteCharactersToMakeFancyString.java)                                                        |                                                                                                                                   |
+| 1961 | [Check If String Is a Prefix of Array](https://leetcode.com/problems/check-if-string-is-a-prefix-of-array)                                                |                                                          [![Java](assets/java.png)](src/CheckIfStringIsAPrefixOfArray.java)                                                          |                                                                                                                                   |
+| 1967 | [Number of Strings That Appear as Substrings in Word](https://leetcode.com/problems/number-of-strings-that-appear-as-substrings-in-word)                  |                                                   [![Java](assets/java.png)](src/NumberOfStringsThatAppearAsSubstringsInWord.java)                                                   |                                                                                                                                   |
+| 1971 | [Find if Path Exists in Graph](https://leetcode.com/problems/find-if-path-exists-in-graph)                                                                |                                                             [![Java](assets/java.png)](src/FindIfPathExistsInGraph.java)                                                             |                                                                                                                                   |
 | 1974 | [Minimum Time to Type Word Using Special Typewriter](https://leetcode.com/problems/minimum-time-to-type-word-using-special-typewriter)                    |                                                                                                                                                                                      |                                                                                                                                   |
 | 1979 | [Find Greatest Common Divisor of Array](https://leetcode.com/problems/find-greatest-common-divisor-of-array)                                              |                                                                                                                                                                                      |                                                                                                                                   |
 | 1984 | [Minimum Difference Between Highest and Lowest of K Scores](https://leetcode.com/problems/minimum-difference-between-highest-and-lowest-of-k-scores)      |                                                                                                                                                                                      |                                                                                                                                   |

src/FindIfPathExistsInGraph.java

@@ -0,0 +1,63 @@
+// https://leetcode.com/problems/find-if-path-exists-in-graph
+// T: O(V + E)
+// S: O(V + E)
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+public class FindIfPathExistsInGraph {
+    public boolean validPath(int n, int[][] edges, int start, int end) {
+        UnDirectedGraph graph = UnDirectedGraph.from(n, edges);
+        return graph.pathFrom(start, end);
+    }
+
+    private static final class UnDirectedGraph {
+        private final Map<Integer, Vertex> vertices = new HashMap<>();
+
+        public static UnDirectedGraph from(int vertices, int[][] edges) {
+            UnDirectedGraph graph = new UnDirectedGraph(vertices);
+            for (int[] edge : edges) {
+                graph.vertices.get(edge[0]).addEdge(edge[1]);
+                graph.vertices.get(edge[1]).addEdge(edge[0]);
+            }
+            return graph;
+        }
+
+        private UnDirectedGraph(int vertices) {
+            for (int i = 0 ; i < vertices ; i++) {
+                this.vertices.put(i, new Vertex(i));
+            }
+        }
+
+        public boolean pathFrom(int start, int end) {
+            return pathTo(vertices.get(start), end, new HashSet<>());
+        }
+
+        private boolean pathTo(Vertex from, int to, Set<Integer> visited) {
+            if (visited.contains(from.value)) return false;
+            if (from.value == to) return true;
+            visited.add(from.value);
+            for (int edge : from.edges) {
+                if (pathTo(vertices.get(edge), to, visited)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        private static final class Vertex {
+            private final int value;
+            private final Set<Integer> edges = new HashSet<>();
+
+            Vertex(int value) {
+                this.value = value;
+            }
+
+            public void addEdge(int to) {
+                edges.add(to);
+            }
+        }
+    }
+}