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Title Description
Given an N-ary tree, whose nodes after the sequence returns from traversing.
Example:
Returns thereafter preorder: [5,6,3,2,4,1].
answer
After the first interpolation preorder (java)
Ideas: The tree is traversed, at the same time to ensure that the head plug preorder. (+ Stack head plug)
/*
// Definition for a Node.
class Node {
public int val;
public List<Node> children;
public Node() {}
public Node(int _val) {
val = _val;
}
public Node(int _val, List<Node> _children) {
val = _val;
children = _children;
}
};
*/
class Solution {
public List<Integer> postorder(Node root) {
LinkedList<Node> stack = new LinkedList<>();
LinkedList<Integer> output = new LinkedList<>();
if (root == null) {
return output;
}
stack.add(root);
while (!stack.isEmpty()) {
Node node = stack.pollLast();
output.addFirst(node.val);
for (Node item : node.children) {
if (item != null) {
stack.add(item);
}
}
}
return output;
}
}
Complexity Analysis
- time complexity:
- Space complexity:
Recursive (java)
Ideas:
class Solution {
public List<Integer> postorder(Node root) {
List<Integer> res = new ArrayList<Integer>();
if(root == null) return res;
for(Node cur:root.children){
res.addAll(postorder(cur));
}
res.add(root.val);
return res;
}
}
Complexity Analysis
- time complexity:
- Space complexity: