solves #261: Graph Valid Tree in java

Author: anishLearnsToCode

README.md

@@ -225,7 +225,7 @@
 | 258  | [Add Digits](https://leetcode.com/problems/add-digits)                                                                                                                 |                                                               [![Java](assets/java.png)](src/AddDigits.java) [![Python](assets/python.png)](python/add_digits.py)                                                                |                                                                                                                                   |
 | 259  | 🔒 [3Sum Smaller](https://leetcode.com/problems/3sum-smaller)                                                                                                          |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 260  | [Single Number III](https://leetcode.com/problems/single-number-iii)                                                                                                   |                                                                                       [![Java](assets/java.png)](src/SingleNumberIII.java)                                                                                       |                                                                                                                                   |
-| 261  | 🔒 [Graph Valid Tree](https://leetcode.com/problems/graph-valid-tree)                                                                                                  |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 261  | 🔒 [Graph Valid Tree](https://leetcode.com/problems/graph-valid-tree)                                                                                                  |                                                                                       [![Java](assets/java.png)](src/GraphValidTree.java)                                                                                        |                                                                                                                                   |
 | 263  | [Ugly Number](https://leetcode.com/problems/ugly-number)                                                                                                               |                                                              [![Java](assets/java.png)](src/UglyNumber.java) [![Python](assets/python.png)](python/ugly_number.py)                                                               |                                                                                                                                   |
 | 264  | [Ugly Number II](https://leetcode.com/problems/ugly-number-ii)                                                                                                         |                                                                                        [![Java](assets/java.png)](src/UglyNumberII.java)                                                                                         |                                                                                                                                   |
 | 266  | 🔒 [Palindrome Permutation](https://leetcode.com/problems/palindrome-permutation)                                                                                      |                                                                                                                                                                                                                                  |                                                                                                                                   |

src/GraphValidTree.java

@@ -0,0 +1,59 @@
+// https://leetcode.com/problems/graph-valid-tree
+// T: O(N)
+// S: O(N)
+
+public class GraphValidTree {
+    private static final class DisjointSet {
+        private final int[] root, rank;
+
+        public DisjointSet(int size) {
+            root = new int[size];
+            rank = new int[size];
+            for (int i = 0 ; i < size ; i++) {
+                root[i] = i;
+                rank[i] = 1;
+            }
+        }
+
+        public int find(int num) {
+            if (root[num] == num) {
+                return num;
+            }
+            return root[num] = find(root[num]);
+        }
+
+        public boolean areConnected(int x, int y) {
+            return find(x) == find(y);
+        }
+
+        public void union(int x, int y) {
+            final int rootX = find(x), rootY = find(y);
+            if (rootX == rootY) {
+                return;
+            }
+            if (root[rootX] < root[rootY]) {
+                root[rootX] = rootY;
+            } else if (root[rootX] > root[rootY]) {
+                root[rootY] = rootX;
+            } else {
+                root[rootY] = rootX;
+                rank[rootX]++;
+            }
+        }
+    }
+
+    public boolean validTree(int n, int[][] edges) {
+        if (edges.length != n - 1) {
+            return false;
+        }
+
+        final DisjointSet disjointSet = new DisjointSet(n);
+        for (int[] edge : edges) {
+            if (disjointSet.areConnected(edge[0], edge[1])) {
+                return false;
+            }
+            disjointSet.union(edge[0], edge[1]);
+        }
+        return true;
+    }
+}