输出二叉树的右视图

日常看不懂系列

  public TreeNode buildTree(int[] xianxu,int l1,int r1,int[] zhongxu,int l2,int r2){
       if(l1>r1||l2>r2){
           return null;
       }

       TreeNode root=new TreeNode(xianxu[l1]);

       int rootIndex=0;

       for (int i=l2;i<=r2;i++){
           if(zhongxu[i]==xianxu[l1]){
               rootIndex=i;
               break;
           }
       }

       int leftsize=rootIndex-l2;
       int rightsize=r2-rootIndex;
       root.left=buildTree(xianxu,l1+1,l1+leftsize,zhongxu,l2,l2+leftsize-1);
       root.right=buildTree(xianxu,r1-rightsize+1,r1,zhongxu,rootIndex+1,r2);
       return root;
   }

   public ArrayList<Integer> rightSideView(TreeNode root){
       Map<Integer,Integer> mp=new HashMap<Integer,Integer>();
       int max_depth=-1;
       Stack<TreeNode> nodes=new Stack<TreeNode>();
       Stack<Integer> depths=new Stack<Integer>();
       nodes.push(root);
       depths.push(0);
       while (!nodes.isEmpty()){
           TreeNode node=nodes.pop();
           int depth=depths.pop();
           if(node!=null){
               max_depth=Math.max(max_depth,depth);
               if(mp.get(depth)==null) mp.put(depth,node.val);
               nodes.push(node.left);
               nodes.push(node.right);
               depths.push(depth+1);
               depths.push(depth+1);
           }
       }
       ArrayList<Integer> res=new ArrayList<Integer>();

       for (int i=0;i<=max_depth;i++){
           res.add(mp.get(i));
       }

       return res;
   }
   public int[] solve(int[] xianxu,int[] zhongxu){
       if(xianxu.length==0) return new int[0];

       TreeNode root=buildTree(xianxu,0,xianxu.length-1,zhongxu,0,zhongxu.length-1);
       ArrayList<Integer> temp=rightSideView(root);
       int[] res=new int[temp.size()];
       for (int i=0;i< temp.size();i++){
           res[i]=temp.get(i);
       }
       return res;

   }