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46 lines (40 loc) · 1.13 KB
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package leetcode.easy;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.List;
public class P_589 {
private static class Node {
public int val;
public List<Node> children;
}
public List<Integer> preorder(Node root) {
final List<Integer> res = new ArrayList<>();
dfs(root, res);
return res;
}
private static void dfs(Node node, List<Integer> res) {
if (node == null) {
return;
}
res.add(node.val);
for (Node next : node.children) {
dfs(next, res);
}
}
public List<Integer> preorderIterative(Node root) {
final List<Integer> res = new ArrayList<>();
final Deque<Node> stack = new ArrayDeque<>();
if (root != null) {
stack.addFirst(root);
}
while (!stack.isEmpty()) {
final Node curr = stack.removeFirst();
res.add(curr.val);
for (int i = curr.children.size() - 1; i >= 0; i--) {
stack.addFirst(curr.children.get(i));
}
}
return res;
}
}