【LeetCode】71. Simplify Path

最新推荐文章于 2019-07-28 17:50:58 发布

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最新推荐文章于 2019-07-28 17:50:58 发布

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题目：

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"

描述：

给出一个字符串表示unix系统下的路径，尝试输出该路径简化后的结果，要求，

路径必须以 / 开始，不能以 / 结尾，相邻两级目录之间只能有一个 / ，

. 表示当前目录，..表示上级目录，/ 为根目录，其上级目录是 /

分析：

用current标记已简化部分的末尾位置，随后遍历该路径，

分情况讨论，

1，遇到 / 时，若current处不为 / ，则放入 / ，否则不操作

2，若遇到单个 "."（".." 或 ".a" 这种不算单个 "."），则跳过，不处理

3，若遇到 ".." （ “..a” 或 "..." 不算），分情况讨论：

1），若current所在不为根目录，则current回退到上一个 / 的位置处重新开始

2），否则跳过这两个点

4，对于其他情况，认为是路径名，添加到有效的path中

最后注意去掉可能存在的多余的 "/"

样例：

"/..."
"/.a"
"/home/"
"/../"
"/home//foo/"
"/a/./b/../../c/"
"/a/../../b/../c//.//"
"/a//b////c/d//././/.."

代码：（时间复杂度 O （n），空间复杂度O （1），因为只使用了path本身的空间）

class Solution {
public:
    string simplifyPath(string path) {
		int current = 0;
		for (int i = 1; i < path.size(); ++ i) {
			if (path[i] == '/') {
				if (path[current] != '/') {
					path[++ current] = '/';
				}
			} else if (onePoint(path, i)) {//只有一个点
				++ i;
			} else if (twoPoint(path, i)) {//有连续两个点
				if (current) {//若非根目录
					-- current;
					while (path[current] != '/') {
						-- current;
					}
				} else {
					++ i;//跳过这两个点
				}
			} else {//对于其他情况，认为是路径名
				while (i < path.size() && path[i] != '/') {
					path[++ current] = path[i];
					++ i;
				}
				-- i;
			}
		}
		if (!current || path[current] != '/') {
			++ current;
		}
		return path.substr(0, current);
	}
	bool onePoint(const string &s, int index) {
		if (s[index] != '.') {//当前位置不为点
			return false;
		}
		if (index + 1 >= s.size()) {//已到顶部
			return true;
		}
		return s[index + 1] == '/';
	}
	
	bool twoPoint(const string &s, int index) {
		if (s[index] != '.' || index + 1 >= s.size() || s[index + 1] != '.') {//当前位置不为点
			return false;
		}
		++ index;
		
		if (index + 1 >= s.size()) {//已到顶部
			return true;
		}
		return s[index + 1] == '/';
	}
};