W10D1.js

//NOTE: These functions are NOT reliable if there are astral characters
//in the input! Use with UCS-2 strings only.

//Python implementations of the same algorithms for comparison:
// https://gist.github.com/Rosuav/d02bf71f8bb5354327ee8a8e5fb54e3f

//Write an algorithm to check whether any permutation of a string is a
//palindrome (a string which reads the same forwards and backwards).
//Note that this does not use the HashMap class due to a lack of useful
//features such as iteration. The core algorithm would work the same way
//though.
function any_palindromes(word) {
	var letter_count = {};
	for (var i = 0; i < word.length; ++i) {
		letter_count[word[i]] = (letter_count[word[i]]|0) + 1;
	}
	var have_odd = false;
	for (var ltr in letter_count) {
		if (letter_count[ltr] % 2) {
			//There are an odd number of this letter. A
			//palindrome is possible with one such letter, but
			//no more, so flag and carry on.
			if (have_odd) return false;
			have_odd = true;
		}
	}
	return true;
}

//Write an algorithm to group a list of words into anagrams.

function _sortword(word) {
	//Helper function: sort a word into some form of canonical order.
	//The exact order is insignificant and need not be lexicographical,
	//as long as it is utterly consistent: any two anagrams of the same
	//letter sequence must return the same string.
	return word.split('').sort().join('')
}

function group_into_anagrams(words) {
	//Slightly sneaky use of double referencing here. The hashmap and
	//return array contain references to all the same arrays - one is
	//keyed based on the sorted forms, and the other is a simple array.
	var anagrams = {}, ret = [];
	for (var word of words) {
		var key = _sortword(word);
		if (anagrams[key]) anagrams[key].push(word);
		else ret.push(anagrams[key] = [word]);
	}
	return ret;
}