LeetCode 589 N-ary Tree Preorder Traversal
摘要：
給定一顆N 叉樹
的根節點，返回前序遍歷後的陣列.
例 :
給予樹：
1
/ | \
324
/ \
56
將其前序遍歷返回: [1,3,5,6,2,4].
...
給定一顆N 叉樹
的根節點，返回前序遍歷後的陣列.
例 :
給予樹： 1 / | \ 324 / \ 56 將其前序遍歷返回: [1,3,5,6,2,4].
解法
和二叉樹的前序遍歷差不多，需要注意處理好子節點的順序即可。
非遞迴解法：
/*
// Definition for a Node.
class Node {
public int val;
public List<Node> children;
public Node() {}
public Node(int _val,List<Node> _children) {
val = _val;
children = _children;
}
};
*/
class Solution {
public List<Integer> preorder(Node root) {
List<Integer> list = new ArrayList<>();
if (root == null) {
return list;
}
Stack<Node> stack = new Stack<>();
stack.add(root);
while (!stack.isEmpty()) {
root = stack.pop();
list.add(root.val);
for (int i = root.children.size() - 1; i >= 0; i--) {
stack.add(root.children.get(i));
}
}
return list;
}
}
遞迴解法：
/*
// Definition for a Node.
class Node {
public int val;
public List<Node> children;
public Node() {}
public Node(int _val,List<Node> _children) {
val = _val;
children = _children;
}
};
*/
class Solution {
List<Integer> list = new ArrayList<>();
public List<Integer> preorder(Node root) {
if (root == null) {
return list;
}
list.add(root.val);
for (Node child : root.children) {
preorder(child);
}
return list;
}
}
Runtime: 1 ms, faster than 100.00% of Java online submissions for N-ary Tree Preorder Traversal. Memory Usage: 47.9 MB, less than 51.19% of Java online submissions for N-ary Tree Preorder Traversal.