NaryTreePostorderTraversal
NaryTreePostorderTraversal.java 源码
package datastructure.tree.leetcode;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Stack;
/**
* @author roseduan
* @time 2020/9/15 10:16 下午
* @description N叉树的后序遍历
*/
public class NaryTreePostorderTraversal {
private final List<Integer> res = new ArrayList<>();
/**
* 递归
*/
public List<Integer> postorder(Node root) {
if (root == null) {
return res;
}
List<Node> children = root.children;
if (!children.isEmpty()) {
for (Node node : children) {
postorder(node);
}
}
res.add(root.val);
return res;
}
/**
* 迭代
*/
public List<Integer> postorder2(Node root) {
LinkedList<Integer> list = new LinkedList<>();
if (root == null) {
return list;
}
Stack<Node> stack = new Stack<>();
stack.push(root);
while (!stack.empty()) {
Node node = stack.pop();
list.addFirst(node.val);
List<Node> children = node.children;
if (children != null) {
for (Node child : children) {
stack.push(child);
}
}
}
return list;
}
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;
}
};
}
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