Minimum Depth of Binary Tree leetcode

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.

如果一个node的左儿子为空 右儿子不空 从root 到左儿子的路径不算是minimum depth
因为左儿子不算这个node的leaf node
所以要比最大深度那道题要多一个判断
如果左儿子空返回右儿子的deepth 右儿子空返回左儿子deepth

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int minDepth(TreeNode root) {
        if (root == null){
            return 0;
        }
        int left = minDepth(root.left);
        int right = minDepth(root.right);
        if (left == 0) {
            return right + 1;
        }
        if (right == 0) {
            return left + 1;
        }
        return Math.min(left, right) + 1;
    }
}

非递归的做法:

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int minDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        int res = 0;
        while (!queue.isEmpty()){
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                if (node.left == null && node.right == null) {
                    return res + 1;//node已经算入了 所以要+1 
                }
                if (node.left != null) {
                    queue.offer(node.left);
                }
                if (node.right != null) {
                    queue.offer(node.right);
                }
            }
            res += 1;
        }
        return res;
    }
}