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BinaryTreePreorderTraversal.java

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BinaryTreePreorderTraversal.java

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/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

*/

class Solution {

public List<Integer> preorderTraversal(TreeNode root) {

Stack<TreeNode> stack = new Stack<>();

List<Integer> result = new ArrayList<>();

TreeNode p = root;

while (!stack.isEmpty() || p != null) {

if (p != null) {

result.add(p.val);

stack.push(p.right);

p = p.left;

} else {

p = stack.pop();

}

}

return result;

}

}