How to delete duplicates in a string using recursion? - c++

Question

I'm working on a function that uses recursion in order to delete duplicate characters in a string. Problem is, I'm not sure how to keep passing a string along in order to keep comparing adjacent characters without cutting the string somehow. Here's what I have so far:
string stringClean(const string& str)
{
string s1 = str;
if (/*first char == next char*/)
s1.at(/*first char*/) = "";
return stringClean(s1);
else
return s1;
}
As an example, stringClean("yyzzza") should return "yza". Any tips on how I should proceed?

Answer 1

C++
Here's what I just thought about
#include <iostream>
#include <string>
std::string rec(std::string &word, int index);
std::string rec(std::string word) {
if(word.length() <= 1) {
return word;
}
return word[0] + rec(word, 1);
}
std::string rec(std::string &word, int index) {
if(index == word.length()) {
return "";
}
return (word[index] != word[index-1] ? std::string(1, word[index]) : "") + rec(word, index+1);
}
int main() {
std::cout << rec("aaabbbbcccddd") << std::endl;
}
For one line recursion lovers:
std::string rec(std::string &word, int index) {
return index == word.length() ? "" : (word[index] != word[index-1] ? std::string(1, word[index]) : "") + rec(word, index+1);
}

Answer 2

Algorithm:
Start from the leftmost character and remove duplicates at the left corner if there are any.
If the length of the string is zero or one then return the string.
Check the leftmost character in the starting substring. If it is present then
Recur for a string of length n-1 (string without last character).
If the leftmost character is not present in the starting substring, then
Recur for the remaining string and store the unique character.
Implementation:
#include <string>
#include <iostream>
using namespace std;
string removeDups(string s) {
if(s.length() <= 1) return s;
if(s.substr(0, s.length() - 1).find(s.substr(s.length() - 1, s.length())) != string::npos) {
return removeDups(s.substr(0, s.length() - 1));
} else {
return removeDups(s.substr(0, s.length() - 1)) + s.substr(s.length() - 1, s.length());
}
}
int main() {
string s;
cin >> s;
cout << removeDups(s);
return 0;
}