Generating Random Numbers in a Range with Some Exclusions in Java (#14357)

core-java-modules/core-java-numbers-3/src/main/java/com/baeldung/randomnumbers/RandomNumbersGeneratorWithExclusion.java

@@ -0,0 +1,42 @@
+package com.baeldung.randomnumbers;
+
+import java.util.Arrays;
+import java.util.OptionalInt;
+import java.util.Random;
+
+public class RandomNumbersGeneratorWithExclusion {
+
+    public static int getRandomWithExclusionUsingMathRandom(int min, int max, int[] exclude) {
+        Arrays.sort(exclude);
+        int random = min + (int) ((max - min + 1 - exclude.length) * Math.random());
+        for (int ex : exclude) {
+            if (random < ex) {
+                break;
+            }
+            random++;
+        }
+        return random;
+    }
+
+    public static int getRandomNumberWithExclusionUsingNextInt(int min, int max, int[] exclude) {
+        Random rnd = new Random();
+        Arrays.sort(exclude);
+        int random = min + rnd.nextInt(max - min + 1 - exclude.length);
+        for (int ex : exclude) {
+            if (random < ex) {
+                break;
+            }
+            random++;
+        }
+        return random;
+    }
+
+    public int getRandomWithExclusion(int min, int max, int[] exclude) {
+        Random rnd = new Random();
+        OptionalInt random = rnd.ints(min, max + 1)
+          .filter(num -> Arrays.stream(exclude).noneMatch(ex -> num == ex))
+          .findFirst();
+        return random.orElse(min);
+    }
+
+}