257. Binary Tree Paths

, ,

DFS

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class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> list = new LinkedList<>();
        Deque<Integer> path = new LinkedList<>();

        dfs(list, path, root);

        return list;
    }

    private void dfs(List<String> list, Deque<Integer> path, TreeNode node) {
        if (node == null) {
            return;
        }

        path.add(node.val);

        if (node.left == null && node.right == null) {
            list.add(pathToString(path));
        }

        dfs(list, path, node.left);
        dfs(list, path, node.right);
        path.removeLast();
    }

    private String pathToString(Deque<Integer> path) {
        return path.stream().map(String::valueOf).collect(Collectors.joining("->"));
    }
}

BFS

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class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> list = new LinkedList<>();

        Queue<TreeNode> queue = new LinkedList<>();
        Queue<String> pathQueue = new LinkedList<>();
        queue.add(root);
        pathQueue.add(String.valueOf(root.val));

        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            String path = pathQueue.poll();

            if (node.left == null && node.right == null) {
                list.add(path);
            }

            if (node.left != null) {
                queue.add(node.left);
                pathQueue.add(path + "->" + node.left.val);
            }
            if (node.right != null) {
                queue.add(node.right);
                pathQueue.add(path + "->" + node.right.val);
            }
        }

        return list;
    }
}

References

257. Binary Tree Paths