Minimum Depth of Binary Tree

Q:

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Solution:

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public int minDepth(TreeNode root) {        if (root == null)            return 0;        return depth(root);    }    int depth(TreeNode node) {        if (node == null)            return Integer.MAX_VALUE;        if (node.left == null && node.right == null)            return 1;        return Math.min(depth(node.left), depth(node.right)) + 1;    }}

Level order traversal should be faster since it does not need to visit all the nodes.

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public int minDepth(TreeNode root) {        if (root == null)            return 0;        Queue<TreeNode> queue = new LinkedList<TreeNode>();        queue.offer(root);        boolean found = false;        int level = 0;        while (!queue.isEmpty()) {            if (found)                break;            level++;            Queue<TreeNode> levelQueue = new LinkedList<TreeNode>();            while (!queue.isEmpty()) {                TreeNode node = queue.poll();                if (node.left == null && node.right == null)                    found = true;                if (node.left != null)                    levelQueue.offer(node.left);                if (node.right != null)                    levelQueue.offer(node.right);            }            queue = new LinkedList<TreeNode>(levelQueue);        }        return level;    }}