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preorderTraversal.java
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executable file
·50 lines (42 loc) · 1.16 KB
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package stack;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
/**
* 给定一棵二叉树，返回其节点值的前序遍历。
例如：
给定二叉树[1,null,2,3]，
1
\
2
/
3
返回 [1,2,3]。
注意: 递归方法很简单，你可以使用迭代方法来解决吗？
* Created by Administrator on 2018/4/10 0010.
*/
public class preorderTraversal {
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) { val = x; }
}
public List<Integer> preorderTraversal(TreeNode root) {
List<Integer> result=new ArrayList<>();
if(root==null)
return result;
result.add(root.val);
result.addAll(preorderTraversal(root.left));
result.addAll(preorderTraversal(root.right));
return result;
}
public List<Integer> preorderTraversal2(TreeNode root) {
List<Integer> result=new ArrayList<>();
Stack<TreeNode> stack=new Stack<>();
while (root!=null||stack.size()!=0){
result.add(root.val);
}
return result;
}
}