Binary Tree Paths

lc 257

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

For example, given the following binary tree:

   1
 /   \
2     3
 \
  5

All root-to-leaf paths are:

["1->2->5", "1->3"]

简练code

public List<String> binaryTreePaths(TreeNode root) {
    List<String> answer = new ArrayList<String>();
    if (root != null) searchBT(root, "", answer);
    return answer;
}
private void searchBT(TreeNode root, String path, List<String> answer) {
    if (root.left == null && root.right == null) answer.add(path + root.val);
    if (root.left != null) searchBT(root.left, path + root.val + "->", answer);
    if (root.right != null) searchBT(root.right, path + root.val + "->", answer);
}

    public List<String> binaryTreePaths(TreeNode root) {
        List<String> result = new ArrayList<String>();
        if(root == null) return result;
        List<String> left = binaryTreePaths(root.left);
        List<String> right = binaryTreePaths(root.right);
        if(left == null && right == null || left.size() == 0 && right.size() == 0){
                result.add(String.valueOf(root.val));
                return result;
        }
        for(String i : left ){

            StringBuilder sb = new StringBuilder();
            sb.append(root.val);
            sb.append("->");
            sb.append(i);


            result.add(sb.toString());
        }
        for(String i : right){
            StringBuilder sb = new StringBuilder();
            sb.append(root.val);

                sb.append("->");
                sb.append(i);

            result.add(sb.toString());
        }        
        return result;   
    }