DiameterOfBinaryTree.java

package problems.leetcode;

/**
 * https://leetcode.com/problems/diameter-of-binary-tree/
 */
public class DiameterOfBinaryTree {

    private static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int val) {
            this.val = val;
        }

        @Override
        public String toString() {
            return "TreeNode{" + "val=" + val + '}';
        }
    }

    private int diameter;

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

    private int depth(TreeNode node) {
        if (node == null) {
            return 0;
        }

        int leftDepth = depth(node.left), rightDepth = depth(node.right);
        diameter = Math.max(diameter, leftDepth + rightDepth);

        return 1 + Math.max(leftDepth, rightDepth);
    }

    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.left.left = new TreeNode(4);
        root.left.right = new TreeNode(5);
        root.right = new TreeNode(3);

        int diameter = new DiameterOfBinaryTree().diameterOfBinaryTree(root);
        System.out.println(diameter);
    }


}