Add NumberOfRecentCalls task solution

Author: andrei-punko

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

@@ -0,0 +1,51 @@
+package by.andd3dfx.numeric;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * <pre>
+ * <a href="https://leetcode.com/problems/number-of-recent-calls/description/">Task description</a>
+ *
+ * You have a RecentCounter class which counts the number of recent requests within a certain time frame.
+ *
+ * Implement the RecentCounter class:
+ * - RecentCounter() Initializes the counter with zero recent requests.
+ * - int ping(int t) Adds a new request at time t, where t represents some time in milliseconds, and returns the number of requests
+ * that has happened in the past 3000 milliseconds (including the new request). Specifically, return the number of requests that
+ * have happened in the inclusive range [t - 3000, t].
+ *
+ * It is guaranteed that every call to ping uses a strictly larger value of t than the previous call.
+ *
+ * Example 1:
+ *   Input
+ *   ["RecentCounter", "ping", "ping", "ping", "ping"]
+ *   [[], [1], [100], [3001], [3002]]
+ *
+ *   Output
+ *   [null, 1, 2, 3, 3]
+ *
+ * Explanation:
+ *   RecentCounter recentCounter = new RecentCounter();
+ *   recentCounter.ping(1);     // requests = [1], range is [-2999,1], return 1
+ *   recentCounter.ping(100);   // requests = [1, 100], range is [-2900,100], return 2
+ *   recentCounter.ping(3001);  // requests = [1, 100, 3001], range is [1,3001], return 3
+ *   recentCounter.ping(3002);  // requests = [1, 100, 3001, 3002], range is [2,3002], return 3
+ * </pre>
+ */
+public class NumberOfRecentCalls {
+
+    private final Deque<Integer> deque;
+
+    public NumberOfRecentCalls() {
+        deque = new ArrayDeque<>();
+    }
+
+    public int ping(int t) {
+        deque.addLast(t);
+        while (t - deque.peekFirst() > 3000) {
+            deque.removeFirst();
+        }
+        return deque.size();
+    }
+}

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

@@ -0,0 +1,24 @@
+package by.andd3dfx.numeric;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class NumberOfRecentCallsTest {
+
+    private NumberOfRecentCalls numberOfRecentCalls;
+
+    @Before
+    public void setUp() {
+        numberOfRecentCalls = new NumberOfRecentCalls();
+    }
+
+    @Test
+    public void ping() {
+        assertThat(numberOfRecentCalls.ping(1)).isEqualTo(1);     // requests = [1], range is [-2999,1], return 1
+        assertThat(numberOfRecentCalls.ping(100)).isEqualTo(2);   // requests = [1, 100], range is [-2900,100], return 2
+        assertThat(numberOfRecentCalls.ping(3001)).isEqualTo(3);  // requests = [1, 100, 3001], range is [1,3001], return 3
+        assertThat(numberOfRecentCalls.ping(3002)).isEqualTo(3);  // requests = [1, 100, 3001, 3002], range is [2,3002], return 3
+    }
+}