leetcode/#543-diameter-binary-tree.java at main · Eric-Ptn/leetcode · GitHub

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */

class Solution {

	int diameter = 0;

	public int diameterOfBinaryTree(TreeNode root) {
    	height(root);
    	return diameter;
	}

	private int height(TreeNode root){

        	if(root == null){
            	return -1;
        	}

        	int left = height(root.left);
        	int right = height(root.right);

        	int thisHeight = 1 + Math.max(left, right);
        	int thisDiameter = 2 + left + right;

        	diameter = Math.max(diameter, thisDiameter);

        	return thisHeight;

	}
}