* reduce code

* add function overriding
* update test

Author: realDuYuanChao

Maths/FindMax.java

@@ -5,7 +5,7 @@ public class FindMax {
     //Driver
     public static void main(String[] args) {
         int[] array = {2, 4, 9, 7, 19, 94, 5};
-        System.out.println("max = " + findMax(array));
+        assert findMax(array) == 94;
     }
 
     /**

Maths/FindMaxRecursion.java

@@ -6,7 +6,8 @@ public static void main(String[] args) {
         int low = 0;
         int high = array.length - 1;
 
-        System.out.println("max value is " + max(array, low, high));
+        assert max(array, low, high) == 94;
+        assert max(array, array.length) == 94;
     }
 
     /**
@@ -27,6 +28,17 @@ public static int max(int[] array, int low, int high) {
         int leftMax = max(array, low, mid); //get max in [low, mid]
         int rightMax = max(array, mid + 1, high); //get max in [mid+1, high]
 
-        return leftMax >= rightMax ? leftMax : rightMax;
+        return Math.max(leftMax, rightMax);
+    }
+
+    /**
+     * Get max of array using recursion algorithm
+     *
+     * @param array contains elements
+     * @param len   length of given array
+     * @return max value of {@code array}
+     */
+    public static int max(int[] array, int len) {
+        return len == 1 ? array[0] : Math.max(max(array, len - 1), array[len - 1]);
     }
 }

Maths/FindMin.java

@@ -5,7 +5,7 @@ public class FindMin {
     //Driver
     public static void main(String[] args) {
         int[] array = {2, 4, 9, 7, 19, 94, 5};
-        System.out.println("min = " + findMin(array));
+        assert findMin(array) == 2;
     }
 
     /**

Maths/FindMinRecursion.java

@@ -2,11 +2,12 @@
 
 public class FindMinRecursion {
     public static void main(String[] args) {
-        int[] array = {2, 4, 9, 7, 19, 94, 5};
+        int[] array = {2, 4, 9, -7, 19, 94, 5};
         int low = 0;
         int high = array.length - 1;
 
-        System.out.println("min value is " + min(array, low, high));
+        assert min(array, low, high) == -7;
+        assert min(array, array.length) == -7;
     }
 
     /**
@@ -27,6 +28,17 @@ public static int min(int[] array, int low, int high) {
         int leftMin = min(array, low, mid); //get min in [low, mid]
         int rightMin = min(array, mid + 1, high); //get min in [mid+1, high]
 
-        return leftMin <= rightMin ? leftMin : rightMin;
+        return Math.min(leftMin, rightMin);
+    }
+
+    /**
+     * Get min of array using recursion algorithm
+     *
+     * @param array contains elements
+     * @param len   length of given array
+     * @return min value of {@code array}
+     */
+    public static int min(int[] array, int len) {
+        return len == 1 ? array[0] : Math.min(min(array, len - 1), array[len - 1]);
     }
 }