stack_simplify_unix_like_pathnames.cpp

/* C++ program to simplify a Unix 
styled absolute path of a file */
#include <bits/stdc++.h> 
using namespace std; 

// function to simplify a Unix - styled 
// absolute path 
string simplify(string A) 
{ 
	// stack to store the file's names. 
	stack<string> st; 

	// temporary string which stores the extracted 
	// directory name or commands("." / "..") 
	// Eg. "/a/b/../." 
	// dir will contain "a", "b", "..", "."; 
	string dir; 

	// contains resultant simplifies string. 
	string res; 

	// every string starts from root directory. 
	res.append("/"); 

	// stores length of input string. 
	int len_A = A.length(); 

	for (int i = 0; i < len_A; i++) { 

		// we will clear the temporary string 
		// every time to accomodate new directory 
		// name or command. 
		dir.clear(); 

		// skip all the multiple '/' Eg. "/////"" 
		while (A[i] == '/') 
			i++; 

		// stores directory's name("a", "b" etc.) 
		// or commands("."/"..") into dir 
		while (i < len_A && A[i] != '/') { 
			dir.push_back(A[i]); 
			i++; 
		} 

		// if dir has ".." just pop the topmost 
		// element if the stack is not empty 
		// otherwise ignore. 
		if (dir.compare("..") == 0) { 
			if (!st.empty()) 
				st.pop();			 
		} 

		// if dir has "." then simply continue 
		// with the process. 
		else if (dir.compare(".") == 0) 
			continue; 
		
		// pushes if it encounters directory's 
		// name("a", "b"). 
		else if (dir.length() != 0) 
			st.push(dir);		 
	} 

	// a temporary stack (st1) which will contain 
	// the reverse of original stack(st). 
	stack<string> st1; 
	while (!st.empty()) { 
		st1.push(st.top()); 
		st.pop(); 
	} 

	// the st1 will contain the actual res. 
	while (!st1.empty()) { 
		string temp = st1.top(); 
		
		// if it's the last element no need 
		// to append "/" 
		if (st1.size() != 1) 
			res.append(temp + "/"); 
		else
			res.append(temp); 

		st1.pop(); 
	} 

	return res; 
} 

// Driver code. 
int main() 
{ 
	// absolute path which we have to simplify. 
	string str = "/a/./b/../../c/"; 
	string res = simplify(str); 
	cout << res; 
	return 0; 
}