二叉树的最大深度

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.

 

题意：给定一个二叉树，返回最大深度

 

思路：这里也是用了BFS，只是用depth来记录深度，每遍历一层，深度加1

 

class Solution {
public: //迭代，BFS，自顶向下，利用队列
    int maxDepth(TreeNode* root) {
        if(root==NULL) return 0;
        int depth=0;
        queue<TreeNode *> q;
        q.push(root);
        while(!q.empty()){
            depth++;
            int n=q.size();
            for(int i=0;i<n;i++){
                TreeNode * t=q.front();
                q.pop();
                if(t->left) q.push(t->left);
                if(t->right) q.push(t->right);
            }
        }
        return depth;
    }
};