Leetcod刷题（17）——257. 二叉树的所有路径

输入:

   1
 /   \
2     3
 \
  5

输出: ["1->2->5", "1->3"]

解释: 所有根节点到叶子节点的路径为: 1->2->5, 1->3

 public static List<String> binaryTreePaths1(LeetCodeUtils.TreeNode root) {
        List<String> list = new ArrayList();
        if (root == null) {
            return list;
        }
        StringBuffer sb = new StringBuffer();
        constructTree1(list, root, sb);
        return list;
    }

    public static void constructTree1(List<String> list, LeetCodeUtils.TreeNode root, StringBuffer sb) {
        if (root == null) {
            return;
        }
        sb.append(root.val);
        if (root.left == null && root.right == null) {
            list.add(sb.toString());
        } else {
            sb.append("->");
            constructTree1(list, root.left, sb);
            constructTree1(list, root.right, sb);
        }
    }

  public static List<String> binaryTreePaths(LeetCodeUtils.TreeNode root) {
        List<String> list = new ArrayList();
        if (root == null) {
            return list;
        }
        constructTree(list, root, "");
        return list;
    }

    public static void constructTree(List<String> list, LeetCodeUtils.TreeNode root, String path) {
        if (root == null) {
            return;
        }
        path += Integer.toString(root.val);
        if (root.left == null && root.right == null) {
            list.add(path);
        } else {
            path += "->";
            constructTree(list, root.left, path);
            constructTree(list, root.right, path);
        }
    }