LeetCode 1448: Count Good Nodes in Binary Tree Solution

Master LeetCode problem 1448 (Count Good Nodes in Binary Tree), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1448. Count Good Nodes in Binary Tree

Medium

Tree Depth-First Search Breadth-First Search Binary Tree

Problem Explanation

Explanation

To solve this problem, we can perform a depth-first search (DFS) traversal of the binary tree while keeping track of the maximum value encountered in the path from the root to the current node. If the current node's value is greater than or equal to the maximum value in the path, we increment the count of good nodes. We then recursively explore the left and right subtrees with the updated maximum value.

Start the DFS traversal from the root node with an initial maximum value of Integer.MIN_VALUE.
Keep track of the count of good nodes encountered during traversal.
At each node, update the maximum value in the path if necessary and check if the current node is a good node.
Recursively explore the left and right subtrees with the updated maximum value.
Return the count of good nodes at the end of traversal.

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 binary tree (recursive stack space).

Solution Code

class Solution {
    public int goodNodes(TreeNode root) {
        return dfs(root, Integer.MIN_VALUE);
    }
    
    private int dfs(TreeNode node, int maxSoFar) {
        if (node == null) {
            return 0;
        }
        
        int count = 0;
        if (node.val >= maxSoFar) {
            count++;
            maxSoFar = node.val;
        }
        
        count += dfs(node.left, maxSoFar);
        count += dfs(node.right, maxSoFar);
        
        return count;
    }
}

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