Solution 1://非递归
public List<Integer> preorderTraversal(TreeNode root) {
List<Integer> result = new ArrayList<>();
if (root == null) {
return result;
}
Stack<TreeNode> stack = new Stack<>();
stack.push(root);
while (!stack.empty()) {
TreeNode node = stack.pop();
result.add(node.val);
if (node.right != null) {
stack.push(node.right);
}
if (node.left != null) {
stack.push(node.left);
}
}
return result;
}
Solution 2：//递归
public class Solution {
List<Integer> result = new ArrayList<>();
public List<Integer> preorderTraversal(TreeNode root) {
if (root != null)
helper(root);
return result;
}
private void helper(TreeNode root) {
result.add(root.val);
if (root.left != null)
helper(root.left);
if (root.right != null)
helper(root.right);
}
}- Traversal Preorder Binary Tree 144traversal preorder binary tree postorder traversal binary tree traversal inorder binary tree traversal binary level order traversal complete 1819c tree binary tree maximum-width-of-binary-tree complete binary 321e tree maximum binary depth tree binary-tree-maximum-path-sum