Add uniform number counting algorithm (#6052)

src/test/java/com/thealgorithms/maths/UniformNumbersTest.java

@@ -0,0 +1,56 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class UniformNumbersTest {
+
+    @Test
+    void testSingleUniformDigitRange() {
+        assertEquals(1, UniformNumbers.countUniformIntegers(1, 1));
+        assertEquals(9, UniformNumbers.countUniformIntegers(1, 9));
+    }
+
+    @Test
+    void testSmallRange() {
+        assertEquals(1, UniformNumbers.countUniformIntegers(10, 11));
+        assertEquals(2, UniformNumbers.countUniformIntegers(22, 33));
+    }
+
+    @Test
+    void testRangeWithNoUniformNumbers() {
+        assertEquals(0, UniformNumbers.countUniformIntegers(12, 21));
+        assertEquals(0, UniformNumbers.countUniformIntegers(123, 128));
+    }
+
+    @Test
+    void testRangeWithAllUniformNumbers() {
+        assertEquals(9, UniformNumbers.countUniformIntegers(1, 9));
+        assertEquals(18, UniformNumbers.countUniformIntegers(1, 99));
+    }
+
+    @Test
+    void testMultiDigitRangeWithUniformNumbers() {
+        assertEquals(1, UniformNumbers.countUniformIntegers(100, 111));
+        assertEquals(2, UniformNumbers.countUniformIntegers(111, 222));
+    }
+
+    @Test
+    void testExactUniformBoundary() {
+        assertEquals(1, UniformNumbers.countUniformIntegers(111, 111));
+        assertEquals(2, UniformNumbers.countUniformIntegers(111, 222));
+    }
+
+    @Test
+    void testLargeRange() {
+        assertEquals(27, UniformNumbers.countUniformIntegers(1, 999));
+        assertEquals(36, UniformNumbers.countUniformIntegers(1, 9999));
+    }
+
+    @Test
+    void testInvalidRange() {
+        assertEquals(0, UniformNumbers.countUniformIntegers(500, 100));
+        assertEquals(0, UniformNumbers.countUniformIntegers(-100, -1));
+    }
+}