add find min

realDuYuanChao · realDuYuanChao · commit b8ec62e280ef · 2020-09-30T15:41:07.000+08:00
diff --git a/src/main/java/com/examplehub/maths/FindMin.java b/src/main/java/com/examplehub/maths/FindMin.java
@@ -0,0 +1,26 @@
+package com.examplehub.maths;
+
+import java.util.Arrays;
+
+public class FindMin {
+
+    /**
+     * Find min value in array.
+     *
+     * @param numbers the numbers to be find.
+     * @return min value of numbers.
+     */
+    public static int findMin(int[] numbers) {
+        int min = numbers[0];
+        for (int number : numbers) {
+            if (number < min) {
+                min = number;
+            }
+        }
+        return min;
+    }
+
+    public static int findMinSecond(int[] numbers) {
+        return Arrays.stream(numbers).min().getAsInt();
+    }
+}
diff --git a/src/main/java/com/examplehub/maths/FindMinRecursion.java b/src/main/java/com/examplehub/maths/FindMinRecursion.java
@@ -0,0 +1,37 @@
+package com.examplehub.maths;
+
+public class FindMinRecursion {
+
+    /**
+     * Find min value in array using recursion.
+     *
+     * @param numbers the numbers to find.
+     * @param length  the length of array.
+     * @return min value in given array.
+     */
+    public static int min(int[] numbers, int length) {
+        if (length == 1) {
+            return numbers[0];
+        }
+        int temp = min(numbers, length - 1);
+        return Math.min(numbers[length - 1], temp);
+    }
+
+    /**
+     * Find min value in array using recursion.
+     *
+     * @param numbers the numbers to find.
+     * @param left    the left index of sub array.
+     * @param right   the right index of sub array.
+     * @return min value in given array.
+     */
+    public static int min(int[] numbers, int left, int right) {
+        if (right == left) {
+            return numbers[right];
+        }
+        int middle = (left + right) >> 1;
+        int leftMin = min(numbers, left, middle); /* find min in range[left, middle] */
+        int rightMin = min(numbers, middle + 1, right); /* find min in range[middle + 1, right] */
+        return Math.min(leftMin, rightMin);
+    }
+}
diff --git a/src/test/java/com/examplehub/maths/FindMinRecursionTest.java b/src/test/java/com/examplehub/maths/FindMinRecursionTest.java
@@ -0,0 +1,32 @@
+package com.examplehub.maths;
+
+import com.examplehub.utils.RandomUtils;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class FindMinRecursionTest {
+
+    private int[] numbers;
+
+    @BeforeEach
+    void setup() {
+        numbers = RandomUtils.randomInts(-50, 50, 50);
+    }
+
+    @Test
+    void test() {
+        int min = FindMinRecursion.min(numbers, numbers.length);
+        for (int number : numbers) {
+            assertTrue(min <= number);
+        }
+
+        int left = 0;
+        int right = numbers.length - 1;
+        min = FindMinRecursion.min(numbers, left, right);
+        for (int number : numbers) {
+            assertTrue(min <= number);
+        }
+    }
+}
diff --git a/src/test/java/com/examplehub/maths/FindMinTest.java b/src/test/java/com/examplehub/maths/FindMinTest.java
@@ -0,0 +1,32 @@
+package com.examplehub.maths;
+
+import com.examplehub.utils.RandomUtils;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class FindMinTest {
+    private int[] numbers;
+
+    @BeforeEach
+    public void setup() {
+        numbers = RandomUtils.randomInts(-50, 50, 100);
+    }
+
+    @Test
+    void testFindMax() {
+        int min = FindMin.findMin(numbers);
+        for (int number : numbers) {
+            assertTrue(min <= number);
+        }
+    }
+
+    @Test
+    void testFindMaxSecond() {
+        int min = FindMin.findMinSecond(numbers);
+        for (int number : numbers) {
+            assertTrue(min <= number);
+        }
+    }
+}
