problems(java): add “1887. Reduction Operations to Make the Array Elements Equal”

Signed-off-by: Matej Focko <me@mfocko.xyz>

problems/java/reduction-operations-to-make-the-array-elements-equal.java

@@ -0,0 +1,15 @@
+class Solution {
+    public int reductionOperations(int[] nums) {
+        Arrays.sort(nums);
+
+        int counter = 0;
+
+        for (int i = nums.length - 1; i > 0; --i) {
+            if (nums[i - 1] != nums[i]) {
+                counter += nums.length - i;
+            }
+        }
+
+        return counter;
+    }
+}