0071. Simplify Path

Author: coderbean

markdown/0071. Simplify Path.md

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+### [71\. Simplify Path](https://leetcode.com/problems/simplify-path/)
+
+Difficulty: **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. For more information, see: 
+
+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"
+```
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+class Solution {
+    public String simplifyPath(String path) {
+        String[] split = path.split("/");
+        Deque<String> strings = new LinkedList<>(); // 使用双端队列
+        for (String s : split) {
+            if (!s.equals("") && !s.equals(".")) {
+                if (s.equals("..")) {
+                    if (!strings.isEmpty()) {
+                        strings.pop(); // 双端队列可以用作栈，返回上一层目录
+                    }
+                } else {
+                    strings.push(s); // 双端队列压栈写入头部元素
+                }
+            }
+        }
+        if (strings.isEmpty()) {
+            return "/";
+        }
+        StringBuilder stringBuilder = new StringBuilder();
+        while (!strings.isEmpty()) {
+            stringBuilder.append("/");
+            stringBuilder.append(strings.pollLast()); // 出尾部元素
+        }
+        return stringBuilder.toString();
+    }
+}
+```
+![](https://raw.githubusercontent.com/PicGoBed/PicBed/master/20190721232339.png)

src/main/java/leetcode/_71_/Main.java

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+package leetcode._71_;
+
+import java.util.Stack;
+
+/**
+ * Created by zhangbo54 on 2019-03-04.
+ */
+public class Main {
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println(solution.simplifyPath("/home/"));
+        System.out.println(solution.simplifyPath("/../"));
+        System.out.println(solution.simplifyPath("/home//foo/"));
+        System.out.println(solution.simplifyPath("/a/./b/../../c/"));
+        System.out.println(solution.simplifyPath("/a/../../b/../c//.//"));
+        System.out.println(solution.simplifyPath("/a//b////c/d//././/.."));
+    }
+}
+

src/main/java/leetcode/_71_/Solution.java

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+package leetcode._71_;
+
+import java.util.Deque;
+import java.util.LinkedList;
+
+class Solution {
+    public String simplifyPath(String path) {
+        String[] split = path.split("/");
+        Deque<String> strings = new LinkedList<>(); // 使用双端队列
+        for (String s : split) {
+            if (!s.equals("") && !s.equals(".")) {
+                if (s.equals("..")) {
+                    if (!strings.isEmpty()) {
+                        strings.pop(); // 双端队列可以用作栈，返回上一层目录
+                    }
+                } else {
+                    strings.push(s); // 双端队列压栈写入头部元素
+                }
+            }
+        }
+        if (strings.isEmpty()) {
+            return "/";
+        }
+        StringBuilder stringBuilder = new StringBuilder();
+        while (!strings.isEmpty()) {
+            stringBuilder.append("/");
+            stringBuilder.append(strings.pollLast()); // 出尾部元素
+        }
+        return stringBuilder.toString();
+    }
+}

src/main/java/leetcode/_71_/solution.md

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+### [71\. Simplify Path](https://leetcode.com/problems/simplify-path/)
+
+Difficulty: **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. For more information, see: 
+
+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"
+```
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+class Solution {
+    public String simplifyPath(String path) {
+        String[] split = path.split("/");
+        Deque<String> strings = new LinkedList<>(); // 使用双端队列
+        for (String s : split) {
+            if (!s.equals("") && !s.equals(".")) {
+                if (s.equals("..")) {
+                    if (!strings.isEmpty()) {
+                        strings.pop(); // 双端队列可以用作栈，返回上一层目录
+                    }
+                } else {
+                    strings.push(s); // 双端队列压栈写入头部元素
+                }
+            }
+        }
+        if (strings.isEmpty()) {
+            return "/";
+        }
+        StringBuilder stringBuilder = new StringBuilder();
+        while (!strings.isEmpty()) {
+            stringBuilder.append("/");
+            stringBuilder.append(strings.pollLast()); // 出尾部元素
+        }
+        return stringBuilder.toString();
+    }
+}
+```
+![](https://raw.githubusercontent.com/PicGoBed/PicBed/master/20190721232339.png)