Add solution for ValidNumber leetcode task

Author: andrei-punko

src/main/java/by/andd3dfx/numeric/ValidNumber.java

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+package by.andd3dfx.numeric;
+
+/**
+ * <pre>
+ * https://leetcode.com/problems/valid-number/description/
+ *
+ * A valid number can be split up into these components (in order):
+ *
+ *     A decimal number or an integer.
+ *     (Optional) An 'e' or 'E', followed by an integer.
+ *
+ * A decimal number can be split up into these components (in order):
+ *
+ *     (Optional) A sign character (either '+' or '-').
+ *     One of the following formats:
+ *         One or more digits, followed by a dot '.'.
+ *         One or more digits, followed by a dot '.', followed by one or more digits.
+ *         A dot '.', followed by one or more digits.
+ *
+ * An integer can be split up into these components (in order):
+ *
+ *     (Optional) A sign character (either '+' or '-').
+ *     One or more digits.
+ *
+ * For example, all the following are valid numbers: ["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3",
+ * "3e+7", "+6e-1", "53.5e93", "-123.456e789"], while the following are not valid numbers:
+ * ["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"].
+ *
+ * Given a string s, return true if s is a valid number.
+ * </pre>
+ */
+public class ValidNumber {
+
+    public static boolean isNumber(String s) {
+        return s.matches("(\\+|-)?([0-9]+\\.?([0-9]+)?|\\.[0-9]+)((e|E)(\\+|-)?[0-9]+)?");
+    }
+}

src/test/java/by/andd3dfx/numeric/ValidNumberTest.java

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+package by.andd3dfx.numeric;
+
+import org.junit.Test;
+
+import static by.andd3dfx.numeric.ValidNumber.isNumber;
+import static org.junit.Assert.*;
+
+public class ValidNumberTest {
+
+    /**
+     * For example, all the following are valid numbers:
+     * ["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789"],
+     * while the following are not valid numbers:
+     * ["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"].
+     */
+    @Test
+    public void testIsNumber() {
+        assertTrue(isNumber("2"));
+        assertTrue(isNumber("0089"));
+        assertTrue(isNumber("-0.1"));
+        assertTrue(isNumber("+3.14"));
+        assertTrue(isNumber("4."));
+        assertTrue(isNumber("-.9"));
+        assertTrue(isNumber("2e10"));
+        assertTrue(isNumber("-90E3"));
+        assertTrue(isNumber("3e+7"));
+        assertTrue(isNumber("+6e-1"));
+        assertTrue(isNumber("53.5e93"));
+        assertTrue(isNumber("-123.456e789"));
+
+        assertFalse(isNumber("abc"));
+        assertFalse(isNumber("1a"));
+        assertFalse(isNumber("1e"));
+        assertFalse(isNumber("e3"));
+        assertFalse(isNumber("99e2.5"));
+        assertFalse(isNumber("--6"));
+        assertFalse(isNumber("-+3"));
+        assertFalse(isNumber("95a54e53"));
+    }
+}