tree log

    fun main() {
        val root = Environment.getExternalStorageDirectory()
        tree(root)
    }

    private fun tree(dir: File) {
        Log.d("Bob", dir.path)
        dfsLog(dir)
    }

    private fun dfsLog(dir: File, indent: String = "") {
        val files = dir.listFiles() ?: return
        val size = files.size
        files.forEachIndexed { index, file ->
            val last = index == size - 1
            Log.d("Bob", "${indent + if (last) "└─ " else "├─ "}${file.name}")
            dfsLog(file, indent + if (last) "   " else "│  ")
        }
    }

    private fun tree(dir: File, indent: String = "", level: Int = 0) {
        if (level == 0) Log.d("Bob", dir.path)
        val files = dir.listFiles() ?: return
        val size = files.size
        files.forEachIndexed { index, file ->
            val last = index == size - 1
            Log.d("Bob", "${indent + if (last) "└─ " else "├─ "}${file.name}")
            tree(file, indent + if (last) "   " else "│  ", level + 1)
        }
    }

    private fun tree(
        dir: File,
        onLog: (File) -> String = File::getName
    ) {
        Log.d("Bob", dir.path)
        dfsLog(dir, onLog = onLog)
    }

    private fun dfsLog(dir: File, indent: String = "", onLog: (File) -> String) {
        val files = dir.listFiles() ?: return
        val size = files.size
        files.forEachIndexed { index, file ->
            val last = index == size - 1
            Log.d("Bob", "${indent + if (last) "└─ " else "├─ "}${onLog(file)}")
            dfsLog(file, indent + if (last) "   " else "│  ", onLog)
        }
    }

    // 先序遍历非递归（preOrder）
    private fun tree(root: File) {
        Log.d("Bob", root.path)
        // 三元组：文件、日志缩进的前缀、是否是所在文件夹的最后一个文件
        val stack = Stack<Triple<File, String, Boolean>>()
        root.listFiles()?.reversed()?.forEachIndexed { index, file ->
            stack.push(Triple(file, "", index == 0))
        }
        while (stack.isNotEmpty()) {
            val (dir, indent, last) = stack.pop()
            Log.d("Bob", "${indent + if (last) "└─ " else "├─ "}${dir.name}")
            dir.listFiles()?.reversed()?.forEachIndexed { index, file ->
                stack.push(Triple(file, indent + if (last) "   " else "│  ", index == 0))
            }
        }
    }