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0071. Simplify Path

LeetCode真的难系列

发布于：2020年10月30日
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71. Simplify Path Medium

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.

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:

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

Example 2:

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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:

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

Example 4:

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

Example 5:

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

Example 6:

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

思路：

思路一：栈

这两个思路是一样的，只是分别使用数组和栈而已

  • 首先从 / 分开，然后用栈保存，如果栈不为空，且当前字符为 .. 说明要进行进入上层目录，此时将栈中的元素弹出
  • 只要不为空、不为 . 、不为 .. ，就把其中的元素放入栈中即可
  • 最后在最前面和每个字符串中间加上 /

代码：

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public String simplifyPath(String path) {
    // 1. Stack
    String[] split = path.split("/");
    Stack<String> stack = new Stack<>();
    for (String s : split) {
        if (!stack.isEmpty() && "..".equals(s)) {
            stack.pop();
        }
        else if (!".".equals(s) && !"".equals(s) && !"..".equals(s)) {
            stack.push(s);
        }
    }
    List<String> res = new ArrayList<>(stack);
    return "/" + String.join("/", res);
}

时间复杂度：O(n)

空间复杂度：O(n)

思路二：纯数组

代码：

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public String simplifyPath(String path) {
    String[] split = path.split("/");
    List<String> wordList = new ArrayList<>();
    for (String s : split) {
        if (s.isEmpty() || s.equals(".")) {
            continue;
        }
        wordList.add(s);
    }
    List<String> wordListSim = new ArrayList<>();
    for (String s : wordList) {
        if (s.equals("..")) {
            if (!wordListSim.isEmpty()) {
                wordListSim.remove(wordListSim.size() - 1);
            }
        } else {
            wordListSim.add(s);
        }
    }
    return "/" + String.join("/", wordListSim);
}

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本文永久链接是：http://wangba.me/2020/10/30/0071-Simplify-Path/

更新于：2020年10月30日

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