Merge pull request #417 from nikitap492/search

Thanks! Keep it up!

Author: Christian Bender

Searches/src/search/IterativeTernarySearch.java

@@ -0,0 +1,87 @@
+package search;
+
+import java.util.Arrays;
+import java.util.Random;
+import java.util.stream.Stream;
+
+import static java.lang.String.format;
+
+/**
+ *
+ * A iterative version of a ternary search algorithm
+ * This is better way to implement the ternary search, because a recursive version adds some overhead to a stack.
+ * But in java the compile can transform the recursive version to iterative implicitly,
+ * so there are no much differences between these two algorithms
+ *
+ * Worst-case performance	Θ(log3(N))
+ * Best-case performance	O(1)
+ * Average performance	Θ(log3(N))
+ * Worst-case space complexity	O(1)
+ *
+ *
+ * @author Podshivalov Nikita (https://github.com/nikitap492)
+ * @since 2018-04-13
+ *
+ * @see SearchAlgorithm
+ * @see TernarySearch
+ *
+ */
+
+public class IterativeTernarySearch implements SearchAlgorithm {
+
+
+    @Override
+    public <T extends Comparable<T>> int find(T[] array, T key) {
+        int left = 0;
+        int right = array.length - 1;
+
+         while (right > left) {
+
+            int leftCmp =  array[left].compareTo(key);
+            int rightCmp =  array[right].compareTo(key);
+            if (leftCmp == 0) return left;
+            if (rightCmp == 0) return right;
+
+            int leftThird = left + (right - left) / 3 + 1;
+            int rightThird = right - (right - left) / 3 - 1;
+
+
+            if (array[leftThird].compareTo(key) <= 0) {
+                left = leftThird;
+            } else {
+                right = rightThird;
+            }
+        }
+
+        return -1;
+    }
+
+
+    public static void main(String[] args) {
+        //just generate data
+        Random r = new Random();
+        int size = 100;
+        int maxElement = 100000;
+        Integer[] integers = Stream.generate(() -> r.nextInt(maxElement))
+                .limit(size)
+                .sorted()
+                .toArray(Integer[]::new);
+
+
+        //the element that should be found
+        Integer shouldBeFound = integers[r.nextInt(size - 1)];
+
+        IterativeTernarySearch search = new IterativeTernarySearch();
+        int atIndex = search.find(integers, shouldBeFound);
+
+        System.out.println(format("Should be found: %d. Found %d at index %d. An array length %d",
+                shouldBeFound, integers[atIndex], atIndex, size));
+
+        int toCheck = Arrays.binarySearch(integers, shouldBeFound);
+        System.out.println(format("Found by system method at an index: %d. Is equal: %b",
+                toCheck, toCheck == atIndex));
+
+    }
+
+
+}

Sorts/src/sort/SortAlgorithm.java

@@ -4,7 +4,7 @@
 import java.util.List;
 
 /**
- *  The common interface of most algorithms
+ *  The common interface of most sorting algorithms
  *
  * @author Podshivalov Nikita (https://github.com/nikitap492)
  *