LeetCode - Binary Tree Right Side View

Binary Tree Right Side View

//
public List<Integer> rightSideView(TreeNode root) {
        List<Integer> ret = new ArrayList<Integer>();
        helper(ret, root, 0);
        return ret;
    }
    
    private void helper(List<Integer> ret, TreeNode root, int level){
        if(root == null) return;
        if(ret.isEmpty() || level >= ret.size()){
            ret.add(root.val);
        }
        helper(ret, root.right, level + 1);
        helper(ret, root.left, level + 1);
    }
//
public List<Integer> rightSideView(TreeNode root) {
        ArrayList<Integer> ret = new ArrayList<Integer>();
        if(root == null) return ret;
        TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
        helper(map, root, 0);
        Iterator it = map.entrySet().iterator();
        while(it.hasNext()){
            Map.Entry entry = (Map.Entry)it.next();
            ret.add((Integer)entry.getValue());
        }
        return ret;
    }
    
    public void helper(TreeMap<Integer, Integer> map, TreeNode root, int level){
        if(root == null) return;
        helper(map, root.right, level + 1);
        helper(map, root.left, level + 1);
        if(!map.containsKey(level)){
            map.put(level, root.val);
        }
    }

//
public List<Integer> rightSideView(TreeNode root) {
        ArrayList<Integer> ret = new ArrayList<Integer>();
        if(root == null) return ret;
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        helper(map, root, 0);
        Map<Integer, Integer> sortedMap = new TreeMap<Integer, Integer>(map);
        Iterator it = sortedMap.entrySet().iterator();
        while(it.hasNext()){
            Map.Entry entry = (Map.Entry)it.next();
            ret.add((Integer)entry.getValue());
        }
        return ret;
    }
    
    public void helper(HashMap<Integer, Integer> map, TreeNode root, int level){
        if(root == null) return;
        helper(map, root.right, level + 1);
        helper(map, root.left, level + 1);
        if(!map.containsKey(level)){
            map.put(level, root.val);
        }
    }
//
public List<Integer> rightSideView(TreeNode root) {
        List<Integer> ret = new ArrayList<Integer>();
        if(root==null) return ret;
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        helper(root, map, 0);
        if(!map.isEmpty()){
            List<Integer> sortedKeys = new ArrayList<Integer>(map.keySet());
            Collections.sort(sortedKeys);
            for(int i=0; i<sortedKeys.size(); i++){
                ret.add(map.get(sortedKeys.get(i)));
            }
        }
        return ret;
    }
    
    public void helper(TreeNode root, HashMap<Integer, Integer> map, int level){
        if(root == null) return;
        helper(root.right, map, level+1);
        if(!map.containsKey(level)){
            map.put(level, root.val);
        }
        helper(root.left, map, level+1);
    }