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589. N-ary Tree Preorder Traversal
Easy
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Given an n-ary tree, return the preorder traversal of its nodes' values.
For example, given a 3-ary
tree:
Return its preorder traversal as: [1,3,5,6,2,4]
.
递归方法:
/*
// Definition for a Node.
class Node {
public:
int val;
vector<Node*> children;
Node() {}
Node(int _val, vector<Node*> _children) {
val = _val;
children = _children;
}
};
*/
class Solution {
public:
vector<int> preorder(Node* root) {
if(root == NULL){
return Result;
}
Result.push_back(root->val);
for(auto child : root->children){
preorder(child);
}
return Result;
}
private:
vector<int> Result;
};
非递归方法(能减少很多时间)
/*
// Definition for a Node.
class Node {
public:
int val;
vector<Node*> children;
Node() {}
Node(int _val, vector<Node*> _children) {
val = _val;
children = _children;
}
};
*/
class Solution {
public:
vector<int> preorder(Node* root) {
if(root == NULL){return Result;}
s.push(root);
while(!s.empty()){
Node* tmp = s.top();
Result.push_back(tmp->val);
s.pop();
vector<Node*>::reverse_iterator it = tmp->children.rbegin();
for(it;it != tmp->children.rend();it++){
s.push(*it);
}
}
return Result;
}
private:
vector<int> Result;
stack<Node*> s;
};