LeetCode：104_Maximum Depth of Binary Tree | 二叉树的最大深度 | Easy

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.

struct TreeNode {
int            val;
TreeNode*    left;
TreeNode*    right;
TreeNode(int x): val(x), left(NULL),right(NULL) {}
};

//采用DFS的思想
int maxDepth(TreeNode *root)
{
if (NULL == root)
return 0;
int l = maxDepth(root->left);
int r = maxDepth(root->right);

return l > r ? l + 1:r+1;
//以上这两种方式有一种更简便的方法
//return 1 + max(maxDepth(root->left), maxDepth(root->right));
}

//采用BFS的方法，引入队列
int maxDepth(TreeNode *root)
{
if (NULL == root)
return 0;
queue <TreeNode *> que;
int nCount = 1;
int nDepth = 0;// 记录队列里面每一层上的元素

que.push(root);
while(!que.empty()) {
TreeNode *pTemp = que.front();
que.pop();
nCount --;

if (pTemp->left)
que.push(pTemp->left);
if (pTemp->right)
que.push(pTemp->right);

if (nCount == 0) {
nDepth ++;
nCount = que.size();
}
}
return nDepth;
}