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2583-kth-largest-sum-in-a-binary-tree/2583-kth-largest-sum-in-a-binary-tree.java

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+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    public long kthLargestLevelSum(TreeNode root, int k) {
+        if (root == null) return 0L;
+        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
+
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.add(root);
+        while (!queue.isEmpty()) {
+            int levelSize = queue.size(); 
+            ArrayList<Integer> curr = new ArrayList<>(); 
+            for (int i = 0; i < levelSize; i++) {
+                TreeNode node = queue.poll();
+                curr.add(node.val); 
+                if (node.left != null) queue.add(node.left);
+                if (node.right != null) queue.add(node.right);
+            }
+            list.add(curr); 
+        }
+
+        ArrayList<Long> levelSums = new ArrayList<>();
+        for (ArrayList<Integer> level : list) {
+            long sum = 0L;
+            for (int val : level) {
+                sum += val;
+            }
+            levelSums.add(sum);
+        }
+        levelSums.sort((a, b) -> Long.compare(b, a)); 
+
+        return k <= levelSums.size() ? levelSums.get(k - 1) : -1L;
+    }
+}