Solution104.java

package solution101to150;

import common.TreeNode;

import java.util.LinkedList;
import java.util.Queue;
import javafx.util.Pair;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

// Leetcode 104. Maximum Depth of Binary Tree
public class Solution104 {
    // Case 1: Recursion
    public int maxDepth(TreeNode root) {
        return root == null ? 0 : Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
    }

    // Case 2: Iteration
    public int maxDepthIteration(TreeNode root) {
        Queue<Pair<TreeNode, Integer>> stack = new LinkedList<>();
        if (root != null) {
            stack.add(new Pair(root, 1));
        }

        int depth = 0;
        while (!stack.isEmpty()) {
            Pair<TreeNode, Integer> current = stack.poll();
            root = current.getKey();
            int current_depth = current.getValue();
            if (root != null) {
                depth = Math.max(depth, current_depth);
                stack.add(new Pair(root.left, current_depth + 1));
                stack.add(new Pair(root.right, current_depth + 1));
            }
        }
        return depth;
    }
}