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Solution.java
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53 lines (43 loc) · 1.42 KB
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/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
// public List<Integer> preorderTraversal(TreeNode root) {
// List<Integer> result = new ArrayList<Integer>();
// if (root != null)
// preorderTraversal(root, result);
// return result;
// }
// private void preorderTraversal(TreeNode node, List<Integer> result) {
// result.add(node.val);
// if (node.left != null)
// preorderTraversal(node.left, result);
// if (node.right != null)
// preorderTraversal(node.right, result);
// }
//
public List<Integer> preorderTraversal(TreeNode root) {
List<Integer> result = new ArrayList<Integer>();
Stack<TreeNode> stack = new Stack<TreeNode>();
if (root != null) {
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;
}
}