diff --git a/.DS_Store b/.DS_Store
new file mode 100644
index 000000000..add8e05d3
Binary files /dev/null and b/.DS_Store differ
diff --git a/src/recursion.js b/src/recursion.js
index 12ca0a3d7..7d5bb202c 100644
--- a/src/recursion.js
+++ b/src/recursion.js
@@ -4,32 +4,86 @@
 // denoted by n!, is the product of all positive integers less than or equal to n.
 // Example:  5! = 5 x 4 x 3 x 2 x 1 = 120
 // factorial(5);  // 120
-var factorial = function(n) {
+var factorial = function (n, sum = 1, i = n) {
+    if (n < 0) { return null; }
+    if (i === 0) { return sum; }
+    sum *= i;
+    i--;
+    return factorial(n - 1, sum);
 };
 
 // 2. Compute the sum of an array of integers.
 // Example:  sum([1, 2, 3, 4, 5, 6]);  // 21
-var sum = function(array) {
+var sum = function (array, total = 0, i = 0) {
+    if (i >= array.length) {
+        return total;
+    }
+    total += array[i];
+    i++;
+    return sum(array, total, i);
 };
 
 // 3. Sum all numbers in an array containing nested arrays.
 // Example: arraySum([1,[2,3],[[4]],5]); // 15
-var arraySum = function(array) {
+var arraySum = function (array) {
+
 };
 
 // 4. Check if a number is even.
-var isEven = function(n) {
+var isEven = function (n, i = n) {
+    if (i - 2 === 0) {
+        return boolean = true;
+    } else if (i - 2 > 0) {
+        i -= 2;
+        boolean = false;
+        return isEven(n, i, boolean);
+    } else if (i + 2 === 0) {
+        return boolean = true;
+    } else if (i + 2 < 0) {
+        i += 2;
+        boolean = false;
+        return isEven(n, i, boolean);
+    }
+    return boolean;
 };
 
 // 5. Sum all integers below a given integer.
 // sumBelow(10); // 45
 // sumBelow(7); // 21
-var sumBelow = function(n) {
+var sumBelow = function (n, sum = 0, i = n) {
+    if (n === 0) { return sum; }
+    if (n > 0) {
+        i = n - 1;
+        sum += i;
+        i--;
+        return sumBelow(n - 1, sum, i);
+    } else if (n < 0) {
+        i = n + 1;
+        sum += i;
+        i++;
+        return sumBelow(n + 1, sum, i);
+    }
+    return sum;
 };
 
 // 6. Get the integers in range (x, y).
 // Example:  range(2, 9);  // [3, 4, 5, 6, 7, 8]
-var range = function(x, y) {
+var range = function (x, y, arr = []) {
+    if (x === y) { return arr; }
+    if (x > y) {
+        if (y !== x - 1) {
+            x--;
+            arr.push(x);
+            return range(x, y, arr);
+        }
+        return arr; 0.
+    }
+    if (x !== y - 1) {
+        x++;
+        arr.push(x);
+        return range(x, y, arr);
+    }
+    return arr;
 };
 
 // 7. Compute the exponent of a number.
@@ -37,40 +91,84 @@ var range = function(x, y) {
 // 8^2 = 8 x 8 = 64.  Here, 8 is the base and 2 is the exponent.
 // Example:  exponent(4,3);  // 64
 // https://www.khanacademy.org/computing/computer-science/algorithms/recursive-algorithms/a/computing-powers-of-a-number
-var exponent = function(base, exp) {
+var exponent = function (base, exp, i = exp, total = 1) {
+    if (exp === 0) { return 1; }
+    if (exp === 1) { return base; }
+    if (i === 0) { return total; }
+    if (i > 0) {
+        total *= base;
+        i--;
+        return exponent(base, exp, i, total);
+    }
+    if (i < 0) {
+        total /= base;
+        i++;
+        return exponent(base, exp, i, total);
+    }
+    return total;
 };
 
 // 8. Determine if a number is a power of two.
 // powerOfTwo(1); // true
 // powerOfTwo(16); // true
 // powerOfTwo(10); // false
-var powerOfTwo = function(n) {
+var powerOfTwo = function (n, x = 1) {
+    if (x === n) { return true; }
+    if (x > n) { return false; }
+    if (x < n) {
+        x *= 2;
+        return powerOfTwo(n, x);
+    }
 };
 
 // 9. Write a function that accepts a string a reverses it.
-var reverse = function(string) {
+var reverse = function (string) {
+    if (string === "") { return ""; }
+    else {
+        return reverse(string.substr(1)) + string.charAt(0);
+    }
 };
 
 // 10. Write a function that determines if a string is a palindrome.
-var palindrome = function(string) {
-};
+var palindrome = function (string) {
+    if (string.length <= 1) { return true; }
+    if (string[0].toLowerCase() !== string[string.length - 1].toLowerCase()) {
+        return false;
+    }
+    string = string.substr(1, string.length - 2);
+    string = string.replace(' ', '');
+    return palindrome(string);
+}
 
 // 11. Write a function that returns the remainder of x divided by y without using the
 // modulo (%) operator.
 // modulo(5,2) // 1
 // modulo(17,5) // 2
 // modulo(22,6) // 4
-var modulo = function(x, y) {
+var modulo = function (x, y) {
 };
 
 // 12. Write a function that multiplies two numbers without using the * operator  or
 // JavaScript's Math object.
-var multiply = function(x, y) {
+var multiply = function (x, y, i = y, total = 0) {
+    if (x === 0 || y === 0) { return 0; }
+    if (i === 0 && y > 0) { return total; }
+    if (i === 0 && y < 0) { return -total; }
+    if (y > 0) {
+        total += x;
+        i--;
+        return multiply(x, y, i, total);
+    }
+    if (y < 0) {
+        total += x;
+        i++;
+        return multiply(x, y, i, total);
+    }
 };
 
 // 13. Write a function that divides two numbers without using the / operator  or
 // JavaScript's Math object.
-var divide = function(x, y) {
+var divide = function (x, y) {
 };
 
 // 14. Find the greatest common divisor (gcd) of two positive numbers.  The GCD of two
@@ -78,7 +176,7 @@ var divide = function(x, y) {
 // Example:  gcd(4,36);  // 4
 // http://www.cse.wustl.edu/~kjg/cse131/Notes/Recursion/recursion.html
 // https://www.khanacademy.org/computing/computer-science/cryptography/modarithmetic/a/the-euclidean-algorithm
-var gcd = function(x, y) {
+var gcd = function (x, y) {
 };
 
 // 15. Write a function that compares each character of two strings and returns true if
@@ -86,52 +184,90 @@ var gcd = function(x, y) {
 // compareStr('house', 'houses') // false
 // compareStr('', '') // true
 // compareStr('tomato', 'tomato') // true
-var compareStr = function(str1, str2) {
+var compareStr = function (str1, str2, i = 0) {
+    if (i === str1.length && i === str2.length) { return true; }
+    if (str1.charAt(i) !== str2.charAt(i)) {
+        return false;
+    } else if (str1.charAt(i) === str2.charAt(i)) {
+        i++;
+        return compareStr(str1, str2, i);
+    }
+    return true;
 };
 
 // 16. Write a function that accepts a string and creates an array where each letter
 // occupies an index of the array.
-var createArray = function(str){
+var createArray = function (string, i = 0, array = []) {
+    if (i === string.length) { return array; }
+    if (string.charAt(i)) {
+        array.push(string.charAt(i));
+        i++;
+        return createArray(string, i, array);
+    }
+    return array;
 };
 
 // 17. Reverse the order of an array
-var reverseArr = function (array) {
+var reverseArr = function (array, i = array.length - 1, newArr = []) {
+    if (i === -1) { return newArr; }
+    if (i >= 0) {
+        newArr.push(array[i]);
+        i--;
+        return reverseArr(array, i, newArr);
+    }
 };
 
 // 18. Create a new array with a given value and length.
 // buildList(0,5) // [0,0,0,0,0]
 // buildList(7,3) // [7,7,7]
-var buildList = function(value, length) {
+var buildList = function (value, length, i = 0, array = []) {
+    if (i === length) { return array; }
+    array.push(value);
+    i++;
+    return buildList(value, length, i, array);
 };
 
 // 19. Count the occurence of a value inside a list.
 // countOccurrence([2,7,4,4,1,4], 4) // 3
 // countOccurrence([2,'banana',4,4,1,'banana'], 'banana') // 2
-var countOccurrence = function(array, value) {
+var countOccurrence = function (array, value, i = 0, x = 0) {
+    if (i === array.length) { return x; }
+    if (array[i] === value) {
+        i++;
+        x++;
+        return countOccurrence(array, value, i, x);
+    } else {
+        i++;
+        return countOccurrence(array, value, i, x);
+    }
 };
 
 // 20. Write a recursive version of map.
 // rMap([1,2,3], timesTwo); // [2,4,6]
-var rMap = function(array, callback) {
+var rMap = function (array, callback, i = 0, newArr = []) {
+    if (i === array.length) { return newArr; }
+    newArr.push(callback(array[i]));
+    i++;
+    return rMap(array, callback, i, newArr);
 };
 
 // 21. Write a function that counts the number of times a key occurs in an object.
 // var testobj = {'e': {'x':'y'}, 't':{'r': {'e':'r'}, 'p': {'y':'r'}},'y':'e'};
 // countKeysInObj(testobj, 'r') // 1
 // countKeysInObj(testobj, 'e') // 2
-var countKeysInObj = function(obj, key) {
+var countKeysInObj = function (obj, key) {
 };
 
 // 22. Write a function that counts the number of times a value occurs in an object.
 // var testobj = {'e': {'x':'y'}, 't':{'r': {'e':'r'}, 'p': {'y':'r'}},'y':'e'};
 // countValuesInObj(testobj, 'r') // 2
 // countValuesInObj(testobj, 'e') // 1
-var countValuesInObj = function(obj, value) {
+var countValuesInObj = function (obj, value) {
 };
 
 // 23. Find all keys in an object (and nested objects) by a provided name and rename
 // them to a provided new name while preserving the value stored at that key.
-var replaceKeysInObj = function(obj, key, newKey) {
+var replaceKeysInObj = function (obj, key, newKey) {
 };
 
 // 24. Get the first n Fibonacci numbers.  In the Fibonacci Sequence, each subsequent
@@ -139,7 +275,7 @@ var replaceKeysInObj = function(obj, key, newKey) {
 // Example:  0, 1, 1, 2, 3, 5, 8, 13, 21, 34.....
 // fibonacci(5);  // [0, 1, 1, 2, 3, 5]
 // Note:  The 0 is not counted.
-var fibonacci = function(n) {
+var fibonacci = function (n) {
 };
 
 // 25. Return the Fibonacci number located at index n of the Fibonacci sequence.
@@ -147,18 +283,31 @@ var fibonacci = function(n) {
 // nthFibo(5); // 5
 // nthFibo(7); // 13
 // nthFibo(3); // 2
-var nthFibo = function(n) {
+var nthFibo = function (n, i = 0, array = [0, 1]) {
+    if (i === n) { return array[i]; }
+    if (n < 0) { return null; }
+    array.push(array[i] + array[i + 1]);
+    i++;
+    return nthFibo(n, i, array)
 };
 
 // 26. Given an array of words, return a new array containing each word capitalized.
 // var words = ['i', 'am', 'learning', 'recursion'];
 // capitalizedWords(words); // ['I', 'AM', 'LEARNING', 'RECURSION']
-var capitalizeWords = function(input) {
-};
+var capitalizeWords = function (input, array = [], i = 0) {
+    if (input.length === array.length) { return array; }
+    array.push(input[i].toUpperCase());
+    i++;
+    return capitalizeWords(input, array, i);
+}
 
 // 27. Given an array of strings, capitalize the first letter of each index.
 // capitalizeFirst(['car', 'poop', 'banana']); // ['Car', 'Poop', 'Banana']
-var capitalizeFirst = function(array) {
+var capitalizeFirst = function (array, newArr = [], i = 0) {
+    if (array.length === newArr.length) { return newArr; }
+    newArr.push(array[i].charAt(0).toUpperCase() + array[i].slice(1));
+    i++;
+    return capitalizeFirst(array, newArr, i);
 };
 
 // 28. Return the sum of all even numbers in an object containing nested objects.
@@ -170,69 +319,100 @@ var capitalizeFirst = function(array) {
 //   e: {e: {e: 2}, ee: 'car'}
 // };
 // nestedEvenSum(obj1); // 10
-var nestedEvenSum = function(obj) {
+var nestedEvenSum = function (obj) {
 };
 
 // 29. Flatten an array containing nested arrays.
 // Example: flatten([1,[2],[3,[[4]]],5]); // [1,2,3,4,5]
-var flatten = function(arrays) {
+var flatten = function (arrays) {
 };
 
 // 30. Given a string, return an object containing tallies of each letter.
 // letterTally('potato'); // {'p':1, 'o':2, 't':2, 'a':1}
-var letterTally = function(str, obj) {
+var letterTally = function (str, obj = {}, tally = 0, i = 0) {
+    let letters = str.split('');
+    let arrOfObjKeys = Object.keys(obj);
+    if (i === letters.length) { return obj; }
+    if (!obj[letters[i]]) { obj[letters[i]] = 1; }
+    else {
+        obj[letters[i]] += 1;
+    }
+    i++;
+    return letterTally(str, obj, tally, i);
 };
 
+
 // 31. Eliminate consecutive duplicates in a list.  If the list contains repeated
 // elements they should be replaced with a single copy of the element. The order of the
 // elements should not be changed.
 // Example: compress([1, 2, 2, 3, 4, 4, 5, 5, 5]) // [1, 2, 3, 4, 5]
 // Example: compress([1, 2, 2, 3, 4, 4, 2, 5, 5, 5, 4, 4]) // [1, 2, 3, 4, 2, 5, 4]
-var compress = function(list) {
+var compress = function (list, arr = [], i = 0) {
+    if (i === list.length) { return arr; }
+    if (list[i] !== arr[arr.length - 1]) { arr.push(list[i]); }
+    i++;
+    return compress(list, arr, i);
 };
 
 // 32. Augment every element in a list with a new value where each element is an array
 // itself.
 // Example: augmentElements([[],[3],[7]], 5); // [[5],[3,5],[7,5]]
-var augmentElements = function(array, aug) {
+var augmentElements = function (array, aug) {
 };
 
 // 33. Reduce a series of zeroes to a single 0.
 // minimizeZeroes([2,0,0,0,1,4]) // [2,0,1,4]
 // minimizeZeroes([2,0,0,0,1,0,0,4]) // [2,0,1,0,4]
-var minimizeZeroes = function(array) {
+var minimizeZeroes = function(array, arr = [], i= 0, n =1) {
+    if(i === array.length){
+        return arr;
+    }
+    if(array[i] !== array[n]){
+        arr.push(array[i]);
+    }    
+    i++;
+    n++;
+    return minimizeZeroes(array, arr, i , n)
 };
 
+
 // 34. Alternate the numbers in an array between positive and negative regardless of
 // their original sign.  The first number in the index always needs to be positive.
 // alternateSign([2,7,8,3,1,4]) // [2,-7,8,-3,1,-4]
 // alternateSign([-2,-7,8,3,-1,4]) // [2,-7,8,-3,1,-4]
-var alternateSign = function(array) {
+var alternateSign = function (array, i = 0) {
+    i++;
+    var el = array[i];
+    if (i === array.length) { return array; }
+    if (array[0] < 0) { array[0] *= -1; }
+    if (el > 0 && i % 2 === 1) { array[i] = array[i] * -1; }
+    if (el < 0 && i % 2 === 0) { array[i] *= -1; }
+    return alternateSign(array, i);
 };
 
 // 35. Given a string, return a string with digits converted to their word equivalent.
 // Assume all numbers are single digits (less than 10).
 // numToText("I have 5 dogs and 6 ponies"); // "I have five dogs and six ponies"
-var numToText = function(str) {
+var numToText = function (str) {
 };
 
 // *** EXTRA CREDIT ***
 
 // 36. Return the number of times a tag occurs in the DOM.
-var tagCount = function(tag, node) {
+var tagCount = function (tag, node) {
 };
 
 // 37. Write a function for binary search.
 // Sample array:  [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
 // console.log(binarySearch(5)) will return '5'
 
-var binarySearch = function(array, target, min, max) {
+var binarySearch = function (array, target, min, max) {
 };
 
 // 38. Write a merge sort function.
 // Sample array:  [34,7,23,32,5,62]
 // Sample output: [5,7,23,32,34,62]
-var mergeSort = function(array) {
+var mergeSort = function (array) {
 };