LeetCode: Simplify Path

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

For example,
path = "/home/", => "/home"
path = "/a/./b/../../c/", => "/c"

Corner Cases:

• Did you consider the case where path = "/../"?
  In this case, you should return "/".
• Another corner case is the path might contain multiple slashes '/' together, such as "/home//foo/".
  In this case, you should ignore redundant slashes and return "/home/foo".

Solution

Not a difficult problem, but caution needs to be exercised.
Clarify:

1. see ".", stay in the same folder
2. see ".." go back to previous folder

Use a stack to hold folder names and their relationship

	public String simplifyPath(String path) {
	if(path.length()==0) return null;
	if(path.charAt(0) != '/') return null;
	Stack<String> stack = new Stack<String>();
	StringBuilder ret = new StringBuilder();
	int len = path.length();
	for(int i=0; i<len; i++){
	//Skip all '/', such as"/a////b"
	while(i<len&&path.charAt(i)=='/') i++;//out of index error if while(path.charAt(i)=='/'&&i<len)
	if(i==len) break;//!!!forgot
	//collect the string before next '/'
	StringBuilder sb = new StringBuilder();
	while(i<len&&path.charAt(i)!= '/'){
	sb.append(path.charAt(i));
	i++;
	}
	String str = sb.toString();
	if(str.equals("."))//if "." stay in the same folder
	continue;
	else if(str.equals("..")){//if "..", get back to upper folder
	if(!stack.empty())
	stack.pop();
	}//forgot the {}, caused error here
	else//if a folder name, go to next folder
	stack.push(str);
	}
	if(stack.empty()) return "/";
	//construct the file path based on the elements in the stack
	while(!stack.empty()){
	String str = stack.pop();
	ret.insert(0, str);
	ret.insert(0, '/');
	}
	return ret.toString();
	}

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