题目链接

层序遍历

遍历整棵树，当找到一个叶子节点时，直接返回这个叶子节点的深度。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int minDepth(TreeNode root) {
        Deque<TreeNode> queue = new LinkedList<TreeNode>();
        int depth = 1;
        if(root != null){
            queue.offer(root);
        }else{
            return 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 depth;
                }
                if(node.left != null){
                    queue.offer(node.left);
                }
                if(node.right != null){
                    queue.offer(node.right);
                }                
                if(i == size - 1){
                    depth++;
                }
            }
        }
        return depth;
    }
}