二叉树的深度

输入一棵二叉树，求该树的深度。从根结点到叶结点依次经过的结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。

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class Solution { public:     int TreeDepth(TreeNode* pRoot){         if(!pRoot) return 0 ;             return max(1+TreeDepth(pRoot->left), 1+TreeDepth(pRoot->right));     } };

int TreeDepth(TreeNode* pRoot)
    {
     queue<TreeNode*> q;
        if(!pRoot) return 0;
        q.push(pRoot);
        int level=0;
        while(!q.empty()){
            int len=q.size();
            level++;
            while(len--){
                TreeNode* tem=q.front();
                q.pop();
                if(tem->left) q.push(tem->left);
                if(tem->right) q.push(tem->right);
            }
        }
        return level;
    }

非递归写法：层次遍历

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import java.util.Queue; import java.util.LinkedList;   public class Solution {     public int TreeDepth(TreeNode pRoot)     {         if(pRoot == null){             return 0;         }         Queue<TreeNode> queue = new LinkedList<TreeNode>();         queue.add(pRoot);         int depth = 0, count = 0, nextCount = 1;         while(queue.size()!=0){             TreeNode top = queue.poll();             count++;             if(top.left != null){                 queue.add(top.left);             }             if(top.right != null){                 queue.add(top.right);             }             if(count == nextCount){                 nextCount = queue.size();                 count = 0;                 depth++;             }         }         return depth;     } }

递归写法，比较简单，不解释：

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import java.lang.Math; public class Solution {     public int TreeDepth(TreeNode pRoot)     {         if(pRoot == null){             return 0;         }         int left = TreeDepth(pRoot.left);         int right = TreeDepth(pRoot.right);         return Math.max(left, right) + 1;     } }