Depth First Traversal Binary Tree

Question:

Binary Tree Path

Given a binary tree, return all root-to-leaf paths.

  public List<String> binaryTreePaths(TreeNode root) {
        List<String> res=new LinkedList<String>();
        if(root==null) return res;
        dfs(root,""+root.val,res);
        return res;
    }

    public void dfs(TreeNode root, String tmp, List<String> res){
        if(root.left==null&&root.right==null) {
            res.add(tmp);
            return;
        }
        if(root.left!=null) dfs(root.left, tmp+"->"+root.left.val,res);
        if(root.right!=null) dfs(root.right, tmp+"->"+root.right.val, res);
    }

Print out all GrandPa-Father-Me path

public List<String> binaryTreePaths(TreeNode root) {
        List<String> res=new LinkedList<String>();
        if(root==null) return res;
        dfs(root,""+root.val,res,1);
        for(String a:res) System.out.println(a);
        return res;
    }

    public void dfs(TreeNode root,String tmp, List<String> res, int count){
        if(root.left!=null&&count==1) dfs(root.left,""+root.left.val,res,1);
        if(root.right!=null&&count==1) dfs(root.right, ""+root.right.val,res,1);
        if(count==3){
            res.add(tmp);
            return;
        }
        if(root.left!=null) dfs(root.left,tmp+"->"+root.left.val,res,count+1);
        if(root.right!=null) dfs(root.right,tmp+"->"+root.right.val,res,count+1);
    }

Print Ancestors of a given node in Binary Tree

Define function List<Node> getAncestor(Node root, int target)

public List<Node> getAncestor(Node root, int target){
    LinkedList<Node> res=new LinkedList<Node>();
    if(root==null) return res;
    dfs(root,target,res);
    return res;
}

public boolean dfs(TreeNode root, int target, LinkedList<Node> res){
    if(root.val==target) return true;
    res.push(root);
    if(root.left!=null){
        if(dfs(root.left,target,res)) return true;
    }
    if(root.right!=null){
        if(dfs(root.right,target,res) return true;
    }
    res.pop();
}