p257

 

 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class  {
    public List<String> ans = new ArrayList<String>();

	public List<String> binaryTreePaths(TreeNode root) {
		List<Integer> list = new ArrayList<Integer>();
		binaryTreePaths(root, list);
		return ans;
	}

	public void binaryTreePaths(TreeNode root, List<Integer> list) {
		if (root == null)
			return;
		if (root.left == null && root.right == null) {
			list.add(root.val);
			int len = list.size();
			StringBuilder builder = new StringBuilder();
			for (int i = 0; i < len - 1; i++) {
				builder.append(list.get(i) + "->");
			}
			builder.append(list.get(len - 1));
			// System.out.println(sb.toString());
			ans.add(builder.toString());
			// sb.deleteCharAt(sb.length() - 1);
			return;
		}
		list.add(root.val);
		if (root.left != null) {
			binaryTreePaths(root.left, list);
			list.remove(list.size() - 1);
		}

		if (root.right != null) {
			binaryTreePaths(root.right, list);
			list.remove(list.size() - 1);
		}

	}
}