LeetCode_199 Binary Tree Right Side View

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:

Given the following binary tree,

1 <—

/ \

2 3 <—

\ \

5 4 <—

You should return [1, 3, 4].

public List<Integer> rightSideView(TreeNode root) {
List<Integer> re_list = new ArrayList<Integer>();
List<TreeNode> level_list = new ArrayList<TreeNode>();//层序遍历时存储当前层节点的list
List<TreeNode> tmp_list = new ArrayList<TreeNode>();//用来存储下一层节点的list
if(root==null) return re_list;
level_list.add(root);
re_list.add(root.val);
int flag = 1;
while(flag==1) {
flag = 0;
tmp_list.clear();
for(TreeNode node:level_list) {
if(node.left!=null) {
flag = 1;//说明下层还存在节点
tmp_list.add(node.left);
}
if(node.right!=null) {
flag = 1;//说明下层还存在节点
tmp_list.add(node.right);
}
}
int size = tmp_list.size();
if(tmp_list.size()!=0) {
re_list.add(tmp_list.get(size-1).val);//记录当前层最右边节点
level_list.clear();
level_list.addAll(tmp_list);//迭代
}
}
return re_list;
}