原題
LintCode 70. Binary Tree Level Order Traversal II
Description
Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).
Example
Given binary tree {3,9,20,#,#,15,7},
3
/ \
9 20
/ \
15 7
return its bottom-up level order traversal as:
[
[15,7],
[9,20],
[3]
]
代碼
/**
* Definition of TreeNode:
* class TreeNode {
* public:
* int val;
* TreeNode *left, *right;
* TreeNode(int val) {
* this->val = val;
* this->left = this->right = NULL;
* }
* }
*/
class Solution {
public:
/*
* @param root: A tree
* @return: buttom-up level order a list of lists of integer
*/
vector<vector<int>> levelOrderBottom(TreeNode * root) {
// write your code here
vector<vector<int>> res;
if (root == NULL) return res;
queue<TreeNode*> q;
q.push(root);
while (!q.empty()) {
int size = q.size();
vector<int> level;
for (int i = 0; i < size; i++) {
TreeNode *cur = q.front();
q.pop();
level.push_back(cur->val);
if (cur->left) q.push(cur->left);
if (cur->right) q.push(cur->right);
}
res.insert(res.begin(), level);
}
return res;
}
};
