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- Binary Tree Preorder Traversal
题目:对一棵二叉树进行前序遍历,并将结果存在一个List
public class Solution {
public ArrayList<Integer> preorderTraversal(TreeNode root) {
ArrayList<Integer> result = new ArrayList<Integer>();
// null or leaf
if (root == null) {
return result;
}
// Divide
ArrayList<Integer> left = preorderTraversal(root.left);
ArrayList<Integer> right = preorderTraversal(root.right);
// Conquer
result.add(root.val);
result.addAll(left);
result.addAll(right);
return result;
}
}