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题目链接: https://leetcode.com/problems/binary-tree-preorder-traversal/
GitHub答案源代码请点击这里
Recursive解法
class Solution {
public List<Integer> preorderTraversal(TreeNode root) {
List<Integer> res = new ArrayList<>();
dfs(root, res);
return res;
}
private void dfs(TreeNode root, List<Integer> res) {
if (root == null) {
return;
}
res.add(root.val);
dfs(root.left, res);
dfs(root.right, res);
}
}
Iterative解法
class Solution {
public List<Integer> preorderTraversal(TreeNode root) {
if (root == null) {
return new ArrayList<>();
}
List<Integer> res = new ArrayList<>();
Deque<TreeNode> stack = new ArrayDeque<>();
stack.push(root);
TreeNode cur = root;
while (!stack.isEmpty()) {
cur = stack.pop();
res.add(cur.val);
if (cur.right != null) {
stack.push(cur.right);
}
if (cur.left != null) {
stack.push(cur.left);
}
}
return res;
}
}