2022-06-20 update: added "Number of Digit One"

Author: fartem

src/main/java/com/smlnskgmail/jaman/leetcodejava/hard/NumberOfDigitOne.java

@@ -0,0 +1,21 @@
+package com.smlnskgmail.jaman.leetcodejava.hard;
+
+// https://leetcode.com/problems/number-of-digit-one/
+public class NumberOfDigitOne {
+
+    private final int input;
+
+    public NumberOfDigitOne(int input) {
+        this.input = input;
+    }
+
+    public int solution() {
+        int result = 0;
+        for (int i = 1; i <= input; i *= 10) {
+            int div = i * 10;
+            result += (input / div) * i + Math.min(Math.max(input % div - i + 1, 0), i);
+        }
+        return result;
+    }
+
+}

src/test/java/com/smlnskgmail/jaman/leetcodejava/hard/NumberOfDigitOneTest.java

@@ -0,0 +1,17 @@
+package com.smlnskgmail.jaman.leetcodejava.hard;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class NumberOfDigitOneTest {
+
+    @Test
+    public void defaultTest() {
+        assertEquals(
+                6,
+                new NumberOfDigitOne(13).solution()
+        );
+    }
+
+}