题目
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]
]
解答
其实就是个BFS。。。
下面是AC的代码:
/**
* 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>> ans;
vector<vector<TreeNode*>> temp;
int cur_level = 0;
if(root == 0){
return ans;
}
ans.push_back(vector<int>());
ans[0].push_back(root->val);
temp.push_back(vector<TreeNode *>());
temp[0].push_back(root);
int next_level;
int flag = 1;
while(flag){
flag = 0;
next_level = cur_level + 1;
ans.push_back(vector<int>());
temp.push_back(vector<TreeNode *>());
for(vector<TreeNode*>::iterator iter = temp[cur_level].begin(); iter != temp[cur_level].end(); iter++){
if((*iter)->left != 0){
flag = 1;
ans[next_level].push_back((*iter)->left->val);
temp[next_level].push_back((*iter)->left);
}
if((*iter)->right != 0){
flag = 1;
ans[next_level].push_back((*iter)->right->val);
temp[next_level].push_back((*iter)->right);
}
}
cur_level++;
}
ans.pop_back();
return ans;
}
};
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