589.N Ary Tree Preorder Traversal

589.N Ary Tree Preorder Traversal

难度:Easy

给定一个 N 叉树,返回其节点值的前序遍历。

例如,给定一个 3叉树 : 返回其前序遍历: [1,3,5,6,2,4]。

代码如下:

  • 递归版本:

    /*
    // 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) {
    vector<int >res;
    if(!root) return res;
    res.push_back(root->val);
    for(auto i:root->children)
    {
    vector<int>tmp=preorder(i);
    res.insert(res.end(),tmp.begin(),tmp.end());
    }
    return res;
    }
    };
  • 迭代版本:

/*
// 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) {
vector<int>res;
if(!root) return res;
stack<Node*>pt;
pt.push(root);
res.push_back(root->val);
while(!pt.empty())
{
if(pt.top()->children.empty())
{
pt.pop();
if(!pt.empty()) pt.top()->children.erase(pt.top()->children.begin());
}
else{
pt.push(pt.top()->children[0]);
res.push_back(pt.top()->val);
}
}
return res;
}
};