Leetcode 104. 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.

方法一：深度优先搜索，递归版本

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
int maxDepth(TreeNode *root)
{
return root == NULL ? 0 : max(maxDepth(root -> left), maxDepth(root -> right)) + 1;
}

方法二：广度优先搜索，非递归，容易理解

int maxDepth(TreeNode *root)
{
if(root == NULL)
return 0;
int res = 0;
queue<TreeNode *> q;
q.push(root);
while(!q.empty()){
++ res;
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 res;
}