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Time Complexity: O(n), where n is the number of nodes in the binary tree.
Space Complexity: O(h), where h is the height of the tree due to the recursion stack.
1#include <stdlib.h>
2#include <stdio.h>
3
4struct TreeNode {
5 int val;
6 struct TreeNode *left;
7 struct TreeNode *right;
8};
9
10int dfs(struct TreeNode* node, int maxVal) {
11 if (!node) return 0;
12 int total = 0;
13 if (node->val >= maxVal) total = 1;
14 maxVal = (node->val > maxVal) ? node->val : maxVal;
15 total += dfs(node->left, maxVal);
16 total += dfs(node->right, maxVal);
17 return total;
18}
19
20int goodNodes(struct TreeNode* root) {
21 if (!root) return 0;
22 return dfs(root, root->val);
23}
24This solution defines a helper function dfs that performs the depth-first search. It takes parameters for the current node and the maximum value encountered so far. It returns the total count of good nodes.
Time Complexity: O(n), where n is the number of nodes in the tree.
Space Complexity: O(w), where w is the maximum width of the tree.
1
The C solution implements an iterative BFS using a custom queue structure. Each item in the queue stores a node and the maximum value along the path from the root to that node. The algorithm iterates over the queue, evaluating each node's value against the max value, updating good nodes count accordingly.