From 22e2e74bf8149a525d06a01f0fe870fadc2bce71 Mon Sep 17 00:00:00 2001
From: shellhub <shellhub.me@gmail.com>
Date: Wed, 12 Aug 2020 22:51:19 +0800
Subject: [PATCH] add NumberOfDigits

---
 Maths/NumberOfDigits.java | 62 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 Maths/NumberOfDigits.java

diff --git a/Maths/NumberOfDigits.java b/Maths/NumberOfDigits.java
new file mode 100644
index 00000000..9e760727
--- /dev/null
+++ b/Maths/NumberOfDigits.java
@@ -0,0 +1,62 @@
+package Maths;
+
+/**
+ * Find the number of digits in a number.
+ */
+public class NumberOfDigits {
+    public static void main(String[] args) {
+        int[] numbers = {0, 12, 123, 1234, -12345, 123456, 1234567, 12345678, 123456789};
+        for (int i = 0; i < numbers.length; ++i) {
+            assert numberOfDigits(numbers[i]) == i + 1;
+            assert numberOfDigitsFast(numbers[i]) == i + 1;
+            assert numberOfDigitsFaster(numbers[i]) == i + 1;
+            assert numberOfDigitsRecursion(numbers[i]) == i + 1;
+        }
+    }
+
+    /**
+     * Find the number of digits in a number.
+     *
+     * @param number number to find
+     * @return number of digits of given number
+     */
+    private static int numberOfDigits(int number) {
+        int digits = 0;
+        do {
+            digits++;
+            number /= 10;
+        } while (number != 0);
+        return digits;
+    }
+
+    /**
+     * Find the number of digits in a number fast version.
+     *
+     * @param number number to find
+     * @return number of digits of given number
+     */
+    private static int numberOfDigitsFast(int number) {
+        return number == 0 ? 1 : (int) Math.floor(Math.log10(Math.abs(number)) + 1);
+    }
+
+
+    /**
+     * Find the number of digits in a number faster version.
+     *
+     * @param number number to find
+     * @return number of digits of given number
+     */
+    private static int numberOfDigitsFaster(int number) {
+        return number < 0 ? (-number + "").length() : (number + "").length();
+    }
+
+    /**
+     * Find the number of digits in a number using recursion.
+     *
+     * @param number number to find
+     * @return number of digits of given number
+     */
+    private static int numberOfDigitsRecursion(int number) {
+        return number / 10 == 0 ? 1 : 1 + numberOfDigitsRecursion(number / 10);
+    }
+}