Problem:

Given an absolute path for a file (Unix-style), simplify it.

For example,

path = "/home/", => "/home"

path = "/a/./b/../../c/", => "/c"

Analysis:

This problem is very very easy, if you really understand how to read linux path. Big idea:Maintain a stack, then interpret the element between "/" one by one.iff the element is "..", we pop one element outiff the element is ".", we do nothing with it.iff the element is "directory/file name", we push it onto the stack.

Initial Wrong Solution:

public class Solution {    public String simplifyPath(String path) {        if (path == null)            throw new IllegalArgumentException("The passed in path is null!");        String[] stubs = path.split("/");        Stack
     
       stack = new Stack
      
        ();        for (String stub : stubs) {            if (stub.equals("..")) {                if (!stack.isEmpty())                    stack.pop();            } else if (!stub.equals(".")) {                stack.push(stub);            }         }        StringBuffer ret = new StringBuffer();        while (!stack.isEmpty()) {            ret.insert(0, stack.pop());            ret.insert(0, "/");        }        if (ret.charAt(0) != '/')            ret.insert(0, "/");        return ret.toString();    }}
      
     

Mistakes Analysis:

Even though it is easy, I have made following mistakes in implementation.Mistake 1: ignore the case "/", which would result in "no element pushed onto the stack".Then tried following error fix:if (ret.charAt(0) != '/')    ret.insert(0, "/");This is absolutely wrong, since ret is empety, this would cause expcetion.Fix: if (ret.length() == 0)    return "/";Mistake 2: ignore the String.spilit could produce "" as element.Case: "/..."String.split => ["", "..."]Fix:for (String stub : stubs) {    if (stub.equals("..")) {    ...    }}

Solution:

public class Solution {    public String simplifyPath(String path) {        if (path == null)            throw new IllegalArgumentException("The passed in path is null!");        String[] stubs = path.split("/");        Stack
     
       stack = new Stack
      
        ();        for (String stub : stubs) {            if (stub.equals(""))                continue;            if (stub.equals("..")) {                if (!stack.isEmpty())                    stack.pop();            } else if (!stub.equals(".")) {                stack.push(stub);            }         }        StringBuffer ret = new StringBuffer();        while (!stack.isEmpty()) {            ret.insert(0, stack.pop());            ret.insert(0, "/");        }        if (ret.length() == 0)            return "/";        return ret.toString();    }}