C++: Deranged Anagrams

Two or more words are said to be anagrams if they have the same characters, but in a different order. By analogy with derangements we define a deranged anagram as two words with the same characters, but in which the same character does not appear in the same position in both words.

The task is to use the word list at http://www.puzzlers.org/pub/wordlists/unixdict.txt to find and show the longest deranged anagram.

#include <algorithm>
#include <fstream>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <set>
#include <string>

bool is_deranged(const std::string& left, const std::string& right)
{
	return (left.size() == right.size()) &&
	(std::inner_product(left.begin(), left.end(), right.begin(), 0, std::plus<int>(), std::equal_to<char>()) == 0);
}

int main()
{
	std::ifstream input("unixdict.txt");
	if (!input) {
		std::cerr << "can't open input file\n";
		return EXIT_FAILURE;
	}

	typedef std::set<std::string> WordList;
	typedef std::map<std::string, WordList> AnagraMap;
	AnagraMap anagrams;

	std::pair<std::string, std::string> result;
	size_t longest = 0;

	for (std::string value; input >> value; /**/) {
		std::string key(value);
		std::sort(key.begin(), key.end());

		if (longest < value.length()) { // is it a long candidate?
			if (0 < anagrams.count(key)) { // is it an anagram?
				for (const auto& prior : anagrams[key]) {
					if (is_deranged(prior, value)) { // are they deranged?
						result = std::make_pair(prior, value);
						longest = value.length();
					}
				}
			}
		}
		anagrams[key].insert(value);
	}

	std::cout << result.first << ' ' << result.second << '\n';
	return EXIT_SUCCESS;
}