题目:

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

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

click to show corner cases.

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".

代码:

class Solution {
public:
string simplifyPath(string path) {
string result = "";
path.append("/"); // some input path not end with "/"
vector<string> ret; // use vector acting as stack
string tmp_part = "";
ret.push_back(string(,path[]));
for ( size_t i = ; i < path.size(); ++i ){
if ( path[i]=='/' ){
if ( tmp_part==".." ){
if ( ret.size()> )
{
ret.erase(ret.end()-);
ret.erase(ret.end()-);
}
}
else
{
if ( tmp_part!="" && tmp_part!="." )
{
ret.push_back(tmp_part);
ret.push_back("/");
}
}
tmp_part = "";
}
else
{
tmp_part += path[i];
}
}
if ( ret.size()> && ret[ret.size()-]=="/" ) ret.erase(ret.end()-);
for ( size_t i = ; i < ret.size(); ++i ) result += ret[i];
return result;
}
};

tips:

主要思想是stack堆栈的数据结构。

1. 利用"/"来作为间隔判断符号

2. tmp_part为两个"/"之间的字符串部分(需要注意输入的path可能不以"/"结尾,解决办法是人工在path后面补上一个)

3. 如果tmp_part为“..”,则出栈两个元素(前提是栈中元素数目足够)

如果tmp_part不为“.”, 且不为".",且不为"", 则入栈(注意,还要包括后面的“/”)

其他部分靠题目提供的一些corner cases来debug了。

这里用到的一个技巧是vector来代替stack;这样做的好处是返回结果时不用将stack的元素倒序组合。

===============================================

第二次过这道题,大体路子还清晰。有一个地方没有考虑周全:从for退出来时,不能默认最后一个元素直接进栈,需要判断最后一个元素是否合规。

还有,用到stack的,进栈最好检查一下是否符合规定,不符合规定,直接往外弹元素。

class Solution {
public:
string simplifyPath(string path) {
stack<string> sta;
int begin = ;
int len = ;
for ( int i=; i<path.size(); ++i )
{
if ( path[i]!='/' ){
len++;
}
else{
if ( len!= )
{
string tmp = path.substr(begin,len);
if (tmp==".")
{}
else if ( tmp==".." )
{
if (!sta.empty()) sta.pop();
}
else
{
sta.push(path.substr(begin,len));
}
}
begin = i+;
len = ;
}
}
if ( begin<path.size() )
{
if ( len!= )
{
string tmp = path.substr(begin,len);
if (tmp==".")
{}
else if ( tmp==".." )
{
if (!sta.empty()) sta.pop();
}
else
{
sta.push(path.substr(begin,len));
}
}
}
string ret = "";
if (sta.empty()) return "/";
while ( !sta.empty() )
{
ret = "/" + sta.top() + ret;
sta.pop();
}
return ret;
}
};

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