Count and Sum of Nodes

Problem Statement

Pattern:

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Solution

// Count Nodes O(n)
public static int countNodes (Node root) {
	if(root == null) return 0;
	
	int left = countNodes(root.left);
	int right = countNodes(root.right);
	
	return right + left + 1;
}
 
// Sum Nodes O(n)
public static int sumNodes (Node root) {
	if(root == null) return 0;
	
	int leftSum = sumNodes(root.left);
	int rightSum = sumNodes(root.right);
	
	return leftSum + rightSum + root.val;
}

Notes