思路:使用两个队列,一个队列存储当前一层的所有节点,另一个队列存储下一层的节点,结合层次遍历树结构。
code:
class Solution {
public:
vector<vector<int> > levelOrder(TreeNode *root) {
vector<vector<int> > ret;
if(root!=NULL){
TreeNode * temp = root;
queue<TreeNode *> firstQ,nextQ;
firstQ.push(temp);
while(!firstQ.empty()){
vector<int> layerRet;
while(!firstQ.empty()){
TreeNode *t = firstQ.front();
if(t->left != NULL)
nextQ.push(t->left);
if(t->right != NULL)
nextQ.push(t->right);
layerRet.push_back(t->val);
firstQ.pop();
}
firstQ = nextQ;
while(!nextQ.empty())
nextQ.pop();
ret.push_back(layerRet);
}
}
return ret;
}
};