Implementation of ternary search

.gitignore

@@ -4,6 +4,7 @@
 # IDE file
 build/
 .idea/
+*.iml
 
 # gradle directory
 .gradle/

src/main/java/com/ordestiny/tdd/algorithms/TernarySearch.java

@@ -0,0 +1,43 @@
+package com.ordestiny.tdd.algorithms;
+
+public class TernarySearch {
+ public int search(int[] array, int searchNumber) {
+ if (!isSorted(array)) {
+ throw new IllegalArgumentException();
+ }
+
+ int low = 0;
+ int high = array.length - 1;
+
+ while (high >= low) {
+ int mid1 = low + (high - low) / 3;
+ int mid2 = high - (high - low) / 3;
+
+ if (array[mid1] == searchNumber) {
+ return mid1;
+ }
+
+ if (array[mid2] == searchNumber) {
+ return mid2;
+ }
+
+ if (searchNumber > array[mid2]) {
+ low = mid2 + 1;
+ } else if (searchNumber < array[mid1]) {
+ high = mid1 - 1;
+ } else {
+ low = mid1 + 1;
+ high = mid2 - 1;
+ }
+ }
+ return -1;
+ }
+
+ private boolean isSorted(int[] array) {
+ for (int i = 0; i < array.length - 1; i++) {
+ if (array[i] > array[i + 1])
+ return false;
+ }
+ return true;
+ }
+}

src/test/java/com/ordestiny/tdd/algorithms/TernarySearchTest.java

@@ -0,0 +1,48 @@
+package com.ordestiny.tdd.algorithms;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class TernarySearchTest {
+ private final TernarySearch underTest = new TernarySearch();
+
+ @Test
+ public void shouldReturnIndexWhenLowerThird() {
+ assertThat(underTest.search(new int[]{1,2,3,4,5,6,7,8,9,10}, 4)).isEqualTo(3);
+ }
+
+ @Test
+ public void shouldReturnIndexWhenUpperThird() {
+ assertThat(underTest.search(new int[]{1,2,3,4,5,6,7,8,9,10}, 7)).isEqualTo(6);
+ }
+
+ @Test
+ public void shouldReturnIndexUpper() {
+ assertThat(underTest.search(new int[]{1,2,3,4,5,6,7,8,9,10}, 8)).isEqualTo(7);
+ }
+
+ @Test
+ public void shouldReturnIndexLower() {
+ assertThat(underTest.search(new int[]{1,2,3,4,5,6,7,8,9,10}, 1)).isEqualTo(0);
+ }
+
+ @Test
+ public void shouldReturnIndexBetween() {
+ assertThat(underTest.search(new int[]{1,2,3,4,5,6,7,8,9,10}, 5)).isEqualTo(4);
+ }
+
+ @Test
+ public void shouldReturnMinusOneWhenNoMatch() {
+ assertThat(underTest.search(new int[]{1,2,3,4,5,6,7,8,9,10}, 11)).isEqualTo(-1);
+ }
+
+ @Test
+ public void shouldThrowExceptionWhenNotSorted() {
+ assertThatThrownBy(() -> underTest.search(new int[]{10, 9}, 11))
+ .isExactlyInstanceOf(IllegalArgumentException.class);
+ }
+
+
+}