[leetcode 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,#,#,15,7}

,

3
/ \
9  20
/  \
15   7

return its level order traversal as:

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

/**
* Definition for binary tree
* 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> > res;
if (root == NULL) {
return res;
}
vector<TreeNode *> path;
path.push_back(root);
int count = 1;
vector<int> cur;
cur.clear();
while (!path.empty()) {
auto tmp = path.front();
path.erase(path.begin());
count--;
cur.push_back(tmp->val);
if (tmp->left) {
path.push_back(tmp->left);
}
if (tmp->right) {
path.push_back(tmp->right);
}
if (count == 0) {
count = path.size();
res.push_back(cur);
cur.clear();
}
}
return res;
}
};