71. Simplify Path #

Problem #

Given an absolute path for a file (Unix-style), simplify it. Or in other words, convert it to the canonical path.

In a UNIX-style file system, a period . refers to the current directory. Furthermore, a double period .. moves the directory up a level. For more information, see: Absolute path vs relative path in Linux/Unix

Note that the returned canonical path must always begin with a slash /, and there must be only a single slash / between two directory names. The last directory name (if it exists) must not end with a trailing /. Also, the canonical path must be the shortest string representing the absolute path.

Example 1:

Input: "/home/"
Output: "/home"
Explanation: Note that there is no trailing slash after the last directory name.

Example 2:

Input: "/../"
Output: "/"
Explanation: Going one level up from the root directory is a no-op, as the root level is the highest level you can go.

Example 3:

Input: "/home//foo/"
Output: "/home/foo"
Explanation: In the canonical path, multiple consecutive slashes are replaced by a single one.

Example 4:

Input: "/a/./b/../../c/"
Output: "/c"

Example 5:

Input: "/a/../../b/../c//.//"
Output: "/c"

Example 6:

Input: "/a//b////c/d//././/.."
Output: "/a/b/c"

Problem Summary #

Given a Unix file path, simplify this path. This problem also tests the use of a stack.

Solution Approach #

The author submitted this problem many times before passing. It is not that the problem is difficult, but that there are many boundary conditions; missing any one case will cause an error. To see what boundary cases there are, check the author’s test file.

Code #

package leetcode

import (
	"path/filepath"
	"strings"
)

// Solution one
func simplifyPath(path string) string {
	arr := strings.Split(path, "/")
	stack := make([]string, 0)
	var res string
	for i := 0; i < len(arr); i++ {
		cur := arr[i]
		//cur := strings.TrimSpace(arr[i]) A more rigorous approach should also remove trailing spaces
		if cur == ".." {
			if len(stack) > 0 {
				stack = stack[:len(stack)-1]
			}
		} else if cur != "." && len(cur) > 0 {
			stack = append(stack, arr[i])
		}
	}
	if len(stack) == 0 {
		return "/"
	}
	res = strings.Join(stack, "/")
	return "/" + res
}

// Solution two: Golang's official library API
func simplifyPath1(path string) string {
	return filepath.Clean(path)
}