199. Binary Tree Right Side View

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public List<Integer> rightSideView(TreeNode root) {
12         boolean flag=true;
13         List<Integer> list=new ArrayList<>();
14         ArrayList<TreeNode> res=new ArrayList<TreeNode>();
15         Map<Integer,Integer> map=new HashMap<>();
16         
17         if(root==null)
18         return list;
19  
20          res=LevelTraverse(root);
21          list.add(root.val);
22          map.put(0,0);
23          
24         while(flag)
25         {
26        while(root.right!=null)
27        {
28            root=root.right;
29            list.add(root.val);
30            map.put(res.indexOf(root),res.indexOf(root));
31 
32        }
33          if(root.left!=null)
34        {
35            root=root.left;
36            list.add(root.val);
37            map.put(res.indexOf(root),res.indexOf(root));
38        }
39        else{
40             if(res.indexOf(root)-1<0)
41             flag=false;
42             else {
43                 root=res.get(res.indexOf(root)-1);
44                 if(map.containsKey(res.indexOf(root)))
45                 break;
46             }
47        }
48         }
49         return list;
50     }
51     
52     public ArrayList<TreeNode> LevelTraverse(TreeNode root)//树的水平遍历
53     {
54         ArrayList<TreeNode> list=new ArrayList<TreeNode>();
55         Queue<TreeNode> queue = new LinkedList<TreeNode>();
56         queue.add(root);
57         while(queue.size()>0)
58         {
59             TreeNode a=(TreeNode)queue.peek();
60             queue.remove();
61             list.add(a);
62             if(a.left!=null)
63             queue.add(a.left);
64             if(a.right!=null)
65             queue.add(a.right);
66         }
67   
68         return list;
69     }
70 }