Permutations excluding repeated characters

Question

I\'m working on a Free Code Camp problem - http://www.freecodecamp.com/challenges/bonfire-no-repeats-please

The problem description is as follows -

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Answer 1

Thanks Lurai for great suggestion. It took a while and is a bit lengthy but here's my solution (it passes all test cases at FreeCodeCamp after converting to JavaScript of course) - apologies for crappy variables names (learning how to be a bad programmer too ;)) :D

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class PermAlone {

    public static int permAlone(String str) {
        int length = str.length();
        int total = 0;
        int invalid = 0;
        int overlap = 0;
        ArrayList vals = new ArrayList<>();
        Map chars = new HashMap<>();

        // obtain individual characters and their frequencies from the string
        for (int i = 0; i < length; i++) {
            char key = str.charAt(i);
            if (!chars.containsKey(key)) {
                chars.put(key, 1);
            }
            else {
                chars.put(key, chars.get(key) + 1);
            }
        }

        // if one character repeated set total to 0
        if (chars.size() == 1 && length > 1) {
            total = 0;
        }
        // otherwise calculate total, invalid permutations and overlap
        else {
            // calculate total
            total = factorial(length);

            // calculate invalid permutations
            for (char key : chars.keySet()) {
                int len = 0;
                int lenPerm = 0;
                int charPerm = 0;
                int val = chars.get(key);
                int check = 1;
                // if val > 0 there will be more invalid permutations to  calculate
                if (val > 1) {
                    check = val;
                    vals.add(val); 
                }
                while (check > 1) {
                    len = length - check + 1; 
                    lenPerm = factorial(len);
                    charPerm = factorial(check);
                    invalid = lenPerm * charPerm;
                    total -= invalid; 
                    check--; 
                }   
            }

            // calculate overlaps
            if (vals.size() > 1) {
                overlap = factorial(chars.size());
                for (int val : vals) {
                    overlap *= factorial(val);
                }
            }

            total += overlap;
        }
        return total;
    }

    // helper function to calculate factorials - not recursive as I was running out of memory on the platform :?
    private static int factorial(int num) {
        int result = 1;
        if (num == 0 || num == 1) {
            result = num;
        }
        else {
            for (int i = 2; i <= num; i++) {
                result *= i;
            }
        }
        return result;
    }

    public static void main(String[] args) {
        System.out.printf("For %s: %d\n\n", "aab", permAlone("aab")); //   expected 2
        System.out.printf("For %s: %d\n\n", "aaa", permAlone("aaa")); // expected 0
        System.out.printf("For %s: %d\n\n", "aabb", permAlone("aabb")); // expected 8
        System.out.printf("For %s: %d\n\n", "abcdefa", permAlone("abcdefa")); // expected 3600
        System.out.printf("For %s: %d\n\n", "abfdefa", permAlone("abfdefa")); // expected 2640
        System.out.printf("For %s: %d\n\n", "zzzzzzzz", permAlone("zzzzzzzz")); // expected 0
        System.out.printf("For %s: %d\n\n", "a", permAlone("a")); // expected 1
        System.out.printf("For %s: %d\n\n", "aaab", permAlone("aaab")); // expected 0
        System.out.printf("For %s: %d\n\n", "aaabb", permAlone("aaabb")); // expected 12
        System.out.printf("For %s: %d\n\n", "abbc", permAlone("abbc")); //expected 12
    }
}