给定一个二叉树,返回其按层次遍历的节点值。 (即逐层地,从左到右访问所有节点)。
例如:
给定二叉树: [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
返回其层次遍历结果:
[
[3],
[9,20],
[15,7]
]
代码
class Solution {
public:
vector<vector<int> > levelOrder(TreeNode *root) {
vector<vector<int> > res;
if (root == NULL) return res;
queue<TreeNode*> q;
q.push(root);
while (!q.empty()) {
vector<int> oneLevel;
int size = q.size();
for (int i = 0; i < size; ++i) {
TreeNode *node = q.front();
q.pop();
oneLevel.push_back(node->val);
if (node->left) q.push(node->left);
if (node->right) q.push(node->right);
}
res.push_back(oneLevel);
}
return res;
}
};