leetcode--Maximum Depth of Binary Tree

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.

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解题思路：

从根节点root开始，若为NULL则树的深度为0.

若root不为NULL,建立一个队列，放入root，开始循环.

计数自增1(count++),遍历整个队列，每检查一个元素；

若该元素的左节点不为NULL，则将该左节点放入队列；

若该元素的右节点不为NULL，则将该右节点放入队列；

从队列中删除该元素，若队列为空，退出循环

返回计数count

代码：

class Solution {
public:
int maxDepth(TreeNode* root) {
if(root == NULL)
return 0;

int count= 0;
queue<TreeNode *> q;
q.push(root);
while(!q.empty())
{
count++;
for(int i = 0, n = q.size(); i < n; ++ i)
{
TreeNode *p = q.front();
q.pop();

if(p -> left != NULL)
q.push(p -> left);
if(p -> right != NULL)
q.push(p -> right);
}
}

return count;
}
};