NaryTreePreorderTraversal
NaryTreePreorderTraversal.java 源码
package datastructure.tree.leetcode;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Stack;
/**
* @author roseduan
* @time 2020/9/19 10:52 上午
* @description N叉树的前序遍历
*/
public class NaryTreePreorderTraversal {
/**
* 递归
*/
private final List<Integer> res = new ArrayList<>();
public List<Integer> preorder(Node root) {
if (root == null) {
return res;
}
res.add(root.val);
List<Node> children = root.children;
if (children != null) {
for (Node node : children) {
preorder(node);
}
}
return res;
}
/**
* 迭代
*/
public List<Integer> preorder2(Node root) {
List<Integer> list = new ArrayList<>();
if (root == null) {
return list;
}
Stack<Node> stack = new Stack<>();
stack.push(root);
while (!stack.empty()) {
Node node = stack.pop();
list.add(node.val);
List<Node> children = node.children;
if (children != null) {
Collections.reverse(children);
for (Node child : children) {
stack.push(child);
}
}
}
return res;
}
static class Node {
public int val;
public List<Node> children;
public Node(int _val, List<Node> _children) {
val = _val;
children = _children;
}
};
}
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