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Palindrome

AllenWalker (3)
Alright so I'm working on a code to check whether a given word is a palindrome
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#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> ret;

vector<string> find_palindrome ( const string& s)
{
	// Iterator for the first and last character
	string::const_iterator i = s.begin();
	string::const_iterator j = s.end() - 1;

	// Check if the first and last character is the same
	if (*i == *j )
	{ 
		/* If the current pair of character is the same, check the next pair by incrementing i and decrementing j
		   Terminate the loop if the current pair is different or i becomes larger than j (meaning it's a palindrome) */
		while (*i == *j && i <= j)
		{
			++i; --j;
			
			// If i is larger than j, copy the word into ret
			if (i > j) 
			{ 
				ret.push_back(s); 
			} 
		} 

		// reset the iterator for the next word
		i = s.begin();
		j = s.end() - 1;
	}
	return ret;
}

int main()
{ 
	vector<string> palindrome;
	string str; 
	
	while (cin >> str)
	{ 
		find_palindrome(str);
	}

	palindrome = ret;
	sort (palindrome.begin(), palindrome.end());
	vector<string>::const_iterator iter = palindrome.begin();

	cout << "The word that is a palindrome is: " << endl;
	while (iter != palindrome.end())
	{ 
		cout << *iter << endl;
		++iter;
	}

	if (palindrome.size() == 0)
	{
		cout << "No palindrome found" << endl;
	}
}


It works just fine, but the problem is my teacher told me to revise the code by making it more efficient, and not to use the vector<string> ret
Please help me because i don't know how to revise it without using ret..
Last edited on
Cody0023 (336)
well thats easy. just add a vector parameter in the find_palindrome function, and pass palindrome as an argument with the string. Doesnt make sense to assign a global variable to a local one.
AllenWalker (3)
Wow, such a simple solution yet I didn't think of it..
Thank you so much for your help sir!
giblit (3750)
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	// Iterator for the first and last character
	string::const_iterator i = s.begin();
	string::const_iterator j = s.end() - 1;

	// Check if the first and last character is the same
	if (*i == *j )
	{ 
		/* If the current pair of character is the same, check the next pair by incrementing i and decrementing j
		   Terminate the loop if the current pair is different or i becomes larger than j (meaning it's a palindrome) */
		while (*i == *j && i <= j)
		{
			++i; --j;
			
			// If i is larger than j, copy the word into ret
			if (i > j) 
			{ 
				ret.push_back(s); 
			} 
		} 

		// reset the iterator for the next word
		i = s.begin();
		j = s.end() - 1;
	}
Why not simply use reverse iterator and the string constructor?

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bool isPalindrome(std::string const &str)
{
    return str == std::string(str.rbegin(), str.rend());
}


Full example: 
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#include <iostream>
#include <string>
#include <iomanip>

bool isPalindrome(std::string const &str);

int main()
{
    std::cout << std::boolalpha;
    for(std::string const &str : {"apple", "racecar", "mom", "sauce", "redrum", "tattarrattat"})
        std::cout << str << " is palindrome = " << isPalindrome(str) << std::endl;
}

bool isPalindrome(std::string const &str)
{
    return str == std::string(str.rbegin(), str.rend());
}
 
apple is palindrome = false
racecar is palindrome = true
mom is palindrome = true
sauce is palindrome = false
redrum is palindrome = false
tattarrattat is palindrome = true
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