added 4 solutions, READMEs, MIT LICENSE

voicon · Feb 12, 2017 · 5ac5cfb · 5ac5cfb
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diff --git a/10 Days of Statistics/Day 0 - Mean, Median, and Mode/Solution.java b/10 Days of Statistics/Day 0 - Mean, Median, and Mode/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 import java.util.Arrays;
 import java.util.HashMap;

diff --git a/10 Days of Statistics/Day 0 - Weighted Mean/Solution.java b/10 Days of Statistics/Day 0 - Weighted Mean/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 
 public class Solution {

diff --git a/10 Days of Statistics/Day 1 - Interquartile Range/Solution.java b/10 Days of Statistics/Day 1 - Interquartile Range/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 import java.util.Arrays;
 

diff --git a/10 Days of Statistics/Day 1 - Quartiles/Solution.java b/10 Days of Statistics/Day 1 - Quartiles/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 import java.util.Arrays;
 

diff --git a/10 Days of Statistics/Day 1 - Standard Deviation/Solution.java b/10 Days of Statistics/Day 1 - Standard Deviation/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 
 public class Solution {

diff --git a/10 Days of Statistics/Day 2 - Basic Probability/Solution.txt b/10 Days of Statistics/Day 2 - Basic Probability/Solution.txt
@@ -1,3 +1,8 @@
+    Author: Rodney Shaghoulian
+    Github: github.com/rshaghoulian
+HackerRank: hackerrank.com/rshaghoulian
+
+
 Answer: 5/6
 
 There are 6 possibilities on each die. On 2 dice, there are 6 * 6 = 36 possibilities

diff --git a/10 Days of Statistics/Day 2 - Compound Event Probability/Solution.txt b/10 Days of Statistics/Day 2 - Compound Event Probability/Solution.txt
@@ -1,3 +1,8 @@
+    Author: Rodney Shaghoulian
+    Github: github.com/rshaghoulian
+HackerRank: hackerrank.com/rshaghoulian
+
+
 Answer: 17/42
 
 Urn X has a 4/7 probability of giving a red ball

diff --git a/10 Days of Statistics/Day 2 - More Dice/Solution.txt b/10 Days of Statistics/Day 2 - More Dice/Solution.txt
@@ -1,3 +1,8 @@
+    Author: Rodney Shaghoulian
+    Github: github.com/rshaghoulian
+HackerRank: hackerrank.com/rshaghoulian
+
+
 Answer: 1/9
 
 There are 6 possibilities on each die. On 2 dice, there are 6 * 6 = 36 possibilities

diff --git a/10 Days of Statistics/Day 3 - Cards of the Same Suit/Solution.txt b/10 Days of Statistics/Day 3 - Cards of the Same Suit/Solution.txt
@@ -1,3 +1,8 @@
+    Author: Rodney Shaghoulian
+    Github: github.com/rshaghoulian
+HackerRank: hackerrank.com/rshaghoulian
+
+
 Answer: 12/51
 
 There are 13 of each suit in a deck.

diff --git a/10 Days of Statistics/Day 3 - Conditional Probability/Solution.txt b/10 Days of Statistics/Day 3 - Conditional Probability/Solution.txt
@@ -1,3 +1,8 @@
+    Author: Rodney Shaghoulian
+    Github: github.com/rshaghoulian
+HackerRank: hackerrank.com/rshaghoulian
+
+
 Answer: 1/3
 
 ****** 2 valid answers: 1/3 or 1/2

diff --git a/10 Days of Statistics/Day 3 - Drawing Marbles/Solution.txt b/10 Days of Statistics/Day 3 - Drawing Marbles/Solution.txt
@@ -1,3 +1,8 @@
+    Author: Rodney Shaghoulian
+    Github: github.com/rshaghoulian
+HackerRank: hackerrank.com/rshaghoulian
+
+
 Answer: 2/3
 
 After drawing the first marble, we are left with 2 red marbles and 4 blue marbles. Now we calculate the probability of drawing a blue marble as :

diff --git a/10 Days of Statistics/Day 4 - Binomial Distribution I/Solution.java b/10 Days of Statistics/Day 4 - Binomial Distribution I/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 public class Solution {
 
     public static void main(String[] args) {

diff --git a/10 Days of Statistics/Day 4 - Binomial Distribution II/Solution.java b/10 Days of Statistics/Day 4 - Binomial Distribution II/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 public class Solution {
 
     public static void main(String[] args) {

diff --git a/10 Days of Statistics/Day 4 - Geometric Distribution I/Solution.java b/10 Days of Statistics/Day 4 - Geometric Distribution I/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 
 public class Solution {

diff --git a/10 Days of Statistics/Day 4 - Geometric Distribution II/Solution.java b/10 Days of Statistics/Day 4 - Geometric Distribution II/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 
 public class Solution {

diff --git a/10 Days of Statistics/Day 5 - Normal Distribution I/Solution.java b/10 Days of Statistics/Day 5 - Normal Distribution I/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 public class Solution {
 
     public static void main(String[] args) {

diff --git a/10 Days of Statistics/Day 5 - Normal Distribution II/Solution.java b/10 Days of Statistics/Day 5 - Normal Distribution II/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 public class Solution {
 
     public static void main(String[] args) {

diff --git a/10 Days of Statistics/Day 5 - Poisson Distribution I/Solution.java b/10 Days of Statistics/Day 5 - Poisson Distribution I/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 
 public class Solution {

diff --git a/10 Days of Statistics/Day 5 - Poisson Distribution II/Solution.java b/10 Days of Statistics/Day 5 - Poisson Distribution II/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 import java.util.Scanner;
 
 /* Useful Formulas:

diff --git a/10 Days of Statistics/Day 6 - The Central Limit Theorem I/Solution.java b/10 Days of Statistics/Day 6 - The Central Limit Theorem I/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 /* This HackerRank problem has a buggy tutorial (formula is incorrect) and a buggy
    solution (uses the incorrect formula) Hopefully they fix this issue soon.    */
 public class Solution {

diff --git a/10 Days of Statistics/Day 6 - The Central Limit Theorem II/Solution.java b/10 Days of Statistics/Day 6 - The Central Limit Theorem II/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 public class Solution {
 
     public static void main(String[] args) {

diff --git a/10 Days of Statistics/Day 6 - The Central Limit Theorem III/Solution.java b/10 Days of Statistics/Day 6 - The Central Limit Theorem III/Solution.java
@@ -1,3 +1,7 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
 public class Solution {
     public static void main(String[] args) {
         /* Provided variables */

diff --git a/10 Days of Statistics/Day 7 - Pearson Correlation Coefficient I/Solution.java b/10 Days of Statistics/Day 7 - Pearson Correlation Coefficient I/Solution.java
@@ -0,0 +1,64 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
+import java.util.Scanner;
+
+public class Solution {
+
+    public static void main(String[] args) {
+        /* Read and save input */
+        Scanner scan = new Scanner(System.in);
+        int size = scan.nextInt();
+        double [] xs = new double[size];
+        double [] ys = new double[size];
+        for (int i = 0; i < size; i++) {
+            xs[i] = scan.nextDouble();
+        }
+        for (int i = 0; i < size; i++) {
+            ys[i] = scan.nextDouble();
+        }
+
+        System.out.println(pearson(xs, ys));
+    }
+
+    /* Calculates Pearson coefficient */
+    private static Double pearson(double [] xs, double [] ys) {
+        if (xs == null || ys == null || xs.length != ys.length) {
+            return null;
+        }
+        double xMean = getMean(xs);
+        double yMean = getMean(xs);
+        int n = xs.length;
+
+        double numerator = 0;
+        for (int i = 0; i < n; i++) {
+            numerator += (xs[i] - xMean) * (ys[i] - yMean);
+        }
+        return numerator / (n * standardDeviation(xs) * standardDeviation(ys));
+    }
+
+    private static Double getMean(double [] array) {
+        if (array == null) {
+            return null;
+        }
+        double total = 0;
+        for (double num : array) {
+            total += num;
+        }
+        return total / array.length;
+    }
+
+    private static Double standardDeviation(double [] array) {
+        if (array == null) {
+            return null;
+        }
+        double mean = getMean(array);
+        double sum = 0;
+        for (double x : array) {
+            sum += Math.pow(x - mean, 2);
+        }
+        double variance = sum / array.length;
+        return Math.sqrt(variance);
+    }
+}
diff --git a/10 Days of Statistics/Day 7 - Spearman's Rank Correlation Coefficient/Solution.java b/10 Days of Statistics/Day 7 - Spearman's Rank Correlation Coefficient/Solution.java
@@ -0,0 +1,96 @@
+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
+import java.util.Scanner;
+import java.util.Arrays;
+import java.util.Comparator;
+
+/* O(n log n) runtime. O(n) space
+ *
+ * The challenging part is creating the rank arrays.
+ */
+public class Solution {
+
+    public static void main(String[] args) {
+        /* Read and save input */
+        Scanner scan = new Scanner(System.in);
+        int size = scan.nextInt();
+        double [] X = new double[size];
+        double [] Y = new double[size];
+        for (int i = 0; i < size; i++) {
+            X[i] = scan.nextDouble();
+        }
+        for (int i = 0; i < size; i++) {
+            Y[i] = scan.nextDouble();
+        }
+
+        System.out.format("%.3f", spearman(X, Y));
+    }
+
+    /* Calculates Spearman's rank correlation coefficient, */
+    private static Double spearman(double [] X, double [] Y) {
+        /* Error check */
+        if (X == null || Y == null || X.length != Y.length) {
+            return null;
+        }
+
+        /* Create Rank arrays */
+        int [] rankX = getRanks(X);
+        int [] rankY = getRanks(Y);
+
+        /* Apply Spearman's formula */
+        int n = X.length;
+        double numerator = 0;
+        for (int i = 0; i < n; i++) {
+            numerator += Math.pow((rankX[i] - rankY[i]), 2);
+        }
+        numerator *= 6;
+        return 1 - numerator / (n * ((n * n) - 1));
+    }
+
+    /* Returns a new array with ranks. Assumes unique array values. */
+    public static int[] getRanks(double [] array) {
+        int n = array.length;
+
+        /* Create Pair[] and sort by values */
+        Pair [] pair = new Pair[n];
+        for (int i = 0; i < n; i++) {
+            pair[i] = new Pair(i, array[i]);
+        }
+        Arrays.sort(pair, new PairValueComparator());
+
+        /* Create and return ranks[] */
+        int [] ranks = new int[n];
+        int rank = 1;
+        for (Pair p : pair) {
+            ranks[p.index] = rank++;
+        }
+        return ranks;
+    }
+
+    /* A class to store 2 variables */
+    public static class Pair {
+        public final int index;
+        public final double value;
+
+        public Pair(int i, double v) {
+            index = i;
+            value = v;
+        }
+    }
+
+    /* This lets us sort Pairs based on their value field */
+    public static class PairValueComparator implements Comparator<Pair> {
+        @Override
+        public int compare(Pair p1, Pair p2) {
+            if (p1.value < p2.value) {
+                return -1;
+            } else if (p1.value > p2.value) {
+                return 1;
+            } else {
+                return 0;
+            }
+        }
+    }
+}