二叉树深度

dfs遍历每一条路径，比较其大小即可。

public class Solution {
    int max = 0;
    public void dfs(TreeNode root, int deepth){
        if(root==null){
            if(deepth>max){
                max = deepth;
            }
            return;
        }
        dfs(root.left, deepth+1);
        dfs(root.right, deepth+1);
    }
    public int TreeDepth(TreeNode root) {
        dfs(root, 0);
        return max;
    }
}