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Rooted by: Find Largest and Smallest!
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  • Code 
    interface HighLow {

    static int[] findLargestAndSmallest(int[] nums) {
        if (isCollectionEmpty(nums)) return null;

        return findLargestAndSmallestGeneric(nums);
    }

    private static int[] findLargestAndSmallestGeneric(int[] nums) {
        int max = nums[0];
        int min = nums[0];

        for (int num : nums) {
            if (max < num) max = num;
            if (min > num) min = num;
        }

        return new int[]{min, max};
    }

    private static boolean isCollectionEmpty(int[] nums) {
        return nums == null || nums.length == 0;
    }
}
     Test Cases 
    import org.junit.Test;
import static org.junit.Assert.*;
import org.junit.runners.JUnit4;

// TODO: Replace examples and use TDD by writing your own tests

public class SolutionTest {
    
    int[] input = new int[]{-1,-2,-3,-4,-5,-6,-7,-8,-9,-1};
    int[] output = new int[]{-9,-1};
    @Test
    public void allNegatives() {
        assertArrayEquals(output, HighLow.findLargestAndSmallest(input));
    }
  
    int[] input2 = new int[]{1,-2,3,-4,-5,-6,-7,-8,-9};
    int[] output2 = new int[]{-9,3};
    @Test
    public void test2() {
        assertArrayEquals(output2, HighLow.findLargestAndSmallest(input2));
    }
  
    int[] input123 = new int[]{1,2,3};
    int[] output123 = new int[]{1,3};
    @Test
    public void test21() {
        assertArrayEquals(output123, HighLow.findLargestAndSmallest(input123));
    }
  
  int[] input3 = new int[]{4};
  int[] output3 = new int[]{4,4};
  
  @Test
  public void oneItem() {
      assertArrayEquals(output3, HighLow.findLargestAndSmallest(input3));
  }
  
  int[] input4 = new int[]{9,-1};
  int[] output4 = new int[]{-1,9};
  
  @Test
  public void twoItems() {
      assertArrayEquals(output4, HighLow.findLargestAndSmallest(input4));
  }
  
  int[] input5 = new int[]{};
  int[] output5 = null;
  
  @Test
  public void emptyArray() {
      assertArrayEquals(output5, HighLow.findLargestAndSmallest(input5));
  }
  
  int[] input6 = null;
  int[] output6 = null;
  
  @Test
  public void nullInput() {
      assertArrayEquals(output6, HighLow.findLargestAndSmallest(input6));
  }
}
    View Run Output
  • Code
    • interface HighLow {
    • static int[] findLargestAndSmallest(int[] nums) {
    • if (isCollectionEmpty(nums))
    • return null;
    • else if (hasOneElement(nums))
    • return new int[]{nums[0], nums[0]};
    • else if (hasTwoElements(nums))
    • return sortTwoElements(nums);
    • if (isCollectionEmpty(nums)) return null;
    • return findLargestAndSmallestGeneric(nums);
    • }
    • private static int[] findLargestAndSmallestGeneric(int[] nums) {
    • int max = Integer.MIN_VALUE;
    • int min = Integer.MAX_VALUE;
    • int max = nums[0];
    • int min = nums[0];
    • for (int num : nums) {
    • if (max < num)
    • max = num;
    • if (min > num)
    • min = num;
    • if (max < num) max = num;
    • if (min > num) min = num;
    • }
    • return new int[]{min, max};
    • }
    • static boolean hasOneElement(int[] nums) {
    • return nums.length == 1;
    • }
    • static boolean hasTwoElements(int[] nums) {
    • return nums.length == 2;
    • }
    • private static int[] sortTwoElements(int[] nums) {
    • return (nums[0] <= nums[1])
    • ? new int[]{nums[0], nums[1]}
    • : new int[]{nums[1], nums[0]};
    • }
    • private static boolean isCollectionEmpty(int[] nums) {
    • return nums == null || nums.length == 0;
    • }
    • }