102. Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:

Given binary tree

[3,9,20,null,null,15,7]

,

3
/ \
9  20
/  \
15   7

return its level order traversal as:

[
[3],
[9,20],
[15,7]
]

Subscribe to see which companies asked this question

代码：

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int>> levelOrder(TreeNode* root) {
vector<vector<int>> result;
if(root==NULL) return result;
vector<int>temp;
int i=1;
queue<TreeNode*> q;
q.push(root);
while(!q.empty())
{
TreeNode* root=q.front();
q.pop();
temp.push_back(root->val);
if(root->left) q.push(root->left);
if(root->right)q.push(root->right);
--i;
if(i==0)
{
result.push_back(temp);
temp.clear();
i=q.size();
}
}
return result;
}
};