[LeetCode#71]Simplify Path
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 out iff 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<String> stack = new Stack<String> (); 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<String> stack = new Stack<String> (); 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(); } }