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-rw-r--r--kth_largest_sum_binary_tree.c85
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+// 2583. Kth Largest Sum in a Binary Tree
+#include "leetcode.h"
+
+/*
+ * you are given the 'root' of a binary tree and a positive integer 'k'. the
+ * level sum in the tree is the sum of the values of the nodes that are on the
+ * same level. return the k'th largest level sum in the tree (not necessarily
+ * distinct). if there are fewer than 'k' levels in the tree, return -1. note
+ * that two nodes are on the same level if they have the same distance from the
+ * root.
+ */
+
+int depth(struct TreeNode *root) {
+ if (!root)
+ return 0;
+ int l = depth(root->left) + 1;
+ int r = depth(root->right) + 1;
+ return l > r ? l : r;
+}
+
+void level_sum(struct TreeNode *root, int level, long long *data) {
+ if (!root)
+ return;
+ data[level] += root->val;
+ level_sum(root->left, level + 1, data);
+ level_sum(root->right, level + 1, data);
+}
+
+void swap(long long *a, long long *b) {
+ long long tmp = *a;
+ *a = *b;
+ *b = tmp;
+}
+
+int partition(long long *data, int l, int h) {
+ int i = l, j = l;
+ long long pivot = data[h - 1];
+ for (j - l; j < h - 1; j++)
+ if (data[j] < pivot)
+ swap(&data[i++], &data[j]);
+ swap(&data[i], &data[h - 1]);
+ return i;
+}
+
+void quick_select(long long *data, int l, int h, int k) {
+ if (l + 1 < h) {
+ int p = partition(data, l, h);
+ if (p == k)
+ return;
+ else if (p < k)
+ quick_select(data, p + 1, h, k);
+ else
+ quick_select(data, l, p, k);
+ }
+}
+
+long long kthLargestLevelSum(struct TreeNode *root, int k) {
+ int n = depth(root);
+ if (k > n)
+ return -1;
+ long long val, *data = (long long *)calloc(n, sizeof(long long));
+ level_sum(root, 0, data);
+ quick_select(data, 0, n, n - k);
+ return data[n - k];
+}
+
+int main() {
+ struct TreeNode *r1 = treenode_create(5);
+ r1->left = treenode_create(8);
+ r1->right = treenode_create(9);
+ r1->left->left = treenode_create(2);
+ r1->left->right = treenode_create(1);
+ r1->right->left = treenode_create(3);
+ r1->right->right = treenode_create(7);
+ r1->left->left->left = treenode_create(4);
+ r1->left->left->right = treenode_create(6);
+ struct TreeNode *r2 = treenode_create(1);
+ r2->left = treenode_create(2);
+ r2->right = NULL;
+ r2->left->left = treenode_create(3);
+ printf("%lld\n", kthLargestLevelSum(r1, 2)); // expect: 13
+ printf("%lld\n", kthLargestLevelSum(r2, 1)); // expect: 3
+ treenode_free(r1);
+ treenode_free(r2);
+}