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15 changes: 8 additions & 7 deletions java/543-Diameter-of-Binary-Tree.java
Original file line number Diff line number Diff line change
@@ -1,9 +1,12 @@
class Solution {
private static int treeDiameter = 0;

private static int treeDiameter = 0;

public int diameterOfBinaryTree(TreeNode root) {
calculateHeight(root);
return treeDiameter-1;
public int diameterOfBinaryTree(TreeNode root) {
calculateHeight(root);
int result = treeDiameter-1;
treeDiameter = 0;
return Math.max(0, result);
}

private static int calculateHeight(TreeNode currentNode) {
Expand All @@ -13,9 +16,7 @@ private static int calculateHeight(TreeNode currentNode) {
int leftTreeHeight = calculateHeight(currentNode.left);
int rightTreeHeight = calculateHeight(currentNode.right);

// if the current node doesn't have a left or right subtree, we can't have
// a path passing through it, since we need a leaf node on each side
if (leftTreeHeight != 0 && rightTreeHeight != 0) {
if (leftTreeHeight != 0 || rightTreeHeight != 0) {

// diameter at the current node will be equal to the height of left subtree +
// the height of right sub-trees + '1' for the current node
Expand Down