劍指 Offer 32 - II. 從上到下列印二叉樹 II
從上到下按層列印二叉樹,同一層的節點按從左到右的順序列印,每一層列印到一行。
例如:
給定二叉樹: [3,9,20,null,null,15,7],
3
/
9 20
/
15 7
傳回其層次周遊結果:
[
[3],
[9,20],
[15,7]
]
提示:
節點總數 <= 1000
可以在每層用 q.size() 先擷取這一層長度,在 for 循環先解決這一層
/**
* 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>> ans;
if (root == nullptr) return ans;
queue<TreeNode *> q;
q.push(root);
int len = 1;
int nextlen = 0;
vector<int> tmp;
while (!q.empty() && len > 0) {
TreeNode *node = q.front(); q.pop();
len--;
tmp.push_back(node->val);
if (node->left != nullptr) {
q.push(node->left);
nextlen++;
}
if (node->right != nullptr) {
q.push(node->right);
nextlen++;
}
if (len == 0) {
len = nextlen;
nextlen = 0;
vector<int> one(tmp);
ans.push_back(one);
vector<int>().swap(tmp);
}
}
return ans;
}
};