Create kth-largest-sum-in-a-binary-tree.cpp

Author: kamyu104

C++/kth-largest-sum-in-a-binary-tree.cpp

@@ -0,0 +1,31 @@
+// Time:  O(n)
+// Space: O(h)
+
+// bfs, quick select
+class Solution {
+public:
+    long long kthLargestLevelSum(TreeNode* root, int k) {
+        vector<int64_t> arr;
+        vector<TreeNode *> q = {root};
+        while (!empty(q)) {
+            vector<TreeNode *> new_q;
+            for (const auto& u : q) {
+                if (u->left) {
+                    new_q.emplace_back(u->left);
+                }
+                if (u->right) {
+                    new_q.emplace_back(u->right);
+                }
+            }
+            arr.emplace_back(accumulate(cbegin(q), cend(q), 0LL, [](const auto& total, const auto& node) {
+                return total + node->val;
+            }));
+            q = move(new_q);
+        }
+        if (k - 1 >= size(arr)) {
+            return -1;
+        }
+        nth_element(begin(arr), begin(arr) + (k - 1), end(arr), greater<int64_t>());
+        return arr[k - 1];
+    }
+};