add 3249

fishercoder1534 · fishercoder1534 · commit 8a6c4d15512a · 2024-08-10T21:08:02.000-07:00
diff --git a/paginated_contents/algorithms/4th_thousand/README.md b/paginated_contents/algorithms/4th_thousand/README.md
@@ -1,5 +1,6 @@
 | #    | Title                                                                                                                                                               | Solutions                                                                                                                         | Video                                                                         | Difficulty | Tag                                                                  
 |------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------|------------|----------------------------------------------------------------------
+| 3249 | [Count the Number of Good Nodes](https://leetcode.com/problems/count-the-number-of-good-nodes/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3249.java) |                                                                               | Medium     |
 | 3248 | [Snake in Matrix](https://leetcode.com/problems/snake-in-matrix/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3248.java) |                                                                               | Easy       |
 | 3243 | [Shortest Distance After Road Addition Queries I](https://leetcode.com/problems/shortest-distance-after-road-addition-queries-i/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3243.java) |                                                                               | Medium     |
 | 3242 | [Design Neighbor Sum Service](https://leetcode.com/problems/design-neighbor-sum-service/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3242.java) |                                                                               | Easy       |
diff --git a/src/main/java/com/fishercoder/solutions/fourththousand/_3249.java b/src/main/java/com/fishercoder/solutions/fourththousand/_3249.java
@@ -0,0 +1,113 @@
+package com.fishercoder.solutions.fourththousand;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class _3249 {
+    public static class Solution1 {
+        /**
+         * My completely original solution during the contest.
+         */
+        class TreeNode {
+            int val;
+            List<TreeNode> children;
+            int totalChildrenCount;
+
+            public TreeNode(int val) {
+                this.val = val;
+                this.children = new ArrayList<>();
+                this.totalChildrenCount = 1;//count itself as its own child
+            }
+        }
+
+        int goodNodes = 0;
+
+        public int countGoodNodes(int[][] edges) {
+            if (edges == null || edges.length == 0 || edges[0].length == 0) {
+                return 0;
+            }
+            TreeNode root = buildTree(edges);
+            postOrder(root);
+            dfs(root);
+            return goodNodes;
+        }
+
+        private void dfs(TreeNode root) {
+            if (root == null || root.children.isEmpty()) {
+                return;
+            }
+            int size = root.children.get(0).totalChildrenCount;
+            if (size == 0) {
+                return;
+            }
+            boolean possiblyGoodNode = true;
+            for (TreeNode child : root.children) {
+                if (child.totalChildrenCount != size) {
+                    possiblyGoodNode = false;
+                    break;
+                }
+            }
+            if (possiblyGoodNode) {
+                goodNodes++;
+            }
+            for (TreeNode child : root.children) {
+                dfs(child);
+            }
+        }
+
+        private int postOrder(TreeNode root) {
+            if (root == null) {
+                return 0;
+            }
+            if (root.children.isEmpty()) {
+                goodNodes++;
+                return 1;
+            }
+            int totalChildrenCount = 1;
+            for (TreeNode child : root.children) {
+                int count = postOrder(child);
+                totalChildrenCount += count;
+            }
+            root.totalChildrenCount = totalChildrenCount;
+            return totalChildrenCount;
+        }
+
+        private TreeNode buildTree(int[][] edges) {
+            Map<Integer, TreeNode> map = new HashMap<>();
+            for (int i = 0; i < edges.length; i++) {
+                if (edges[i][0] == 0 || edges[i][1] == 0) {
+                    if (edges[i][0] == 0) {
+                        TreeNode parent = map.getOrDefault(edges[i][0], new TreeNode(edges[i][0]));
+                        TreeNode child = map.getOrDefault(edges[i][1], new TreeNode(edges[i][1]));
+                        parent.children.add(child);
+                        map.put(edges[i][0], parent);
+                        map.put(edges[i][1], child);
+                    } else {
+                        TreeNode parent = map.getOrDefault(edges[i][1], new TreeNode(edges[i][1]));
+                        TreeNode child = map.getOrDefault(edges[i][0], new TreeNode(edges[i][0]));
+                        parent.children.add(child);
+                        map.put(edges[i][1], parent);
+                        map.put(edges[i][0], child);
+                    }
+                } else {
+                    if (map.containsKey(edges[i][0])) {
+                        TreeNode parent = map.get(edges[i][0]);
+                        TreeNode child = map.getOrDefault(edges[i][1], new TreeNode(edges[i][1]));
+                        parent.children.add(child);
+                        map.put(edges[i][0], parent);
+                        map.put(edges[i][1], child);
+                    } else if (map.containsKey(edges[i][1])) {
+                        TreeNode parent = map.get(edges[i][1]);
+                        TreeNode child = map.getOrDefault(edges[i][0], new TreeNode(edges[i][0]));
+                        parent.children.add(child);
+                        map.put(edges[i][1], parent);
+                        map.put(edges[i][0], child);
+                    }
+                }
+            }
+            return map.get(0);
+        }
+    }
+}
