Added RateLimiter algorithm.

Author: CunningDJ

RateLimiter.java

@@ -0,0 +1,79 @@
+package com.cunningdj.grokJava;
+
+import java.time.LocalDateTime;
+import java.util.LinkedList;
+import java.time.Duration;
+import java.time.Month;
+
+class RateLimiter {
+	private LinkedList<LocalDateTime> dtQueue;
+	private final int SECONDS_PER_MINUTE = 60;
+	public final int MAX_REQS_PER_MINUTE;
+	// FOR TESTING ONLY (otherwise null)
+	private final LocalDateTime CURRENT_DT_OVERRIDE;
+
+	public RateLimiter(int maxReqsPerMinute) {
+		this.dtQueue = new LinkedList<>();
+		this.MAX_REQS_PER_MINUTE = maxReqsPerMinute;
+		this.CURRENT_DT_OVERRIDE = null;
+	}
+
+	private RateLimiter(int maxReqsPerMinute, LocalDateTime currentDtOverride) {
+		// FOR TESTING ONLY
+		this.dtQueue = new LinkedList<>();
+		this.MAX_REQS_PER_MINUTE = maxReqsPerMinute;
+		this.CURRENT_DT_OVERRIDE = currentDtOverride;
+	}
+
+	// MAIN
+	public static void main(String[] args) {
+		Tester tester = new Tester();
+		String testTitle="";
+
+		// TEST CLASS METHODS HERE USING TESTER CLASS
+		testTitle = "RATE_LIMITER";
+		RateLimiter rl = new RateLimiter(3);
+		tester.isTrue(rl.newRequest(new Request(RateLimiter.makeTestTime(10, 0))), testTitle);
+		tester.isTrue(rl.newRequest(new Request(RateLimiter.makeTestTime(10, 20))), testTitle);
+		tester.isTrue(rl.newRequest(new Request(RateLimiter.makeTestTime(10, 40))), testTitle);
+		// False, and doesn't add it to the queue
+		tester.isFalse(rl.newRequest(new Request(RateLimiter.makeTestTime(10, 59))), testTitle);
+		// True; Skipoed the 10:59 request, and 10:00 request is now > 60s old, leaving 2 within the window during check
+		tester.isTrue(rl.newRequest(new Request(RateLimiter.makeTestTime(11, 01))), testTitle);
+	}
+
+	// PUBLIC
+	public boolean newRequest(Request req) {
+		if (dtQueue.size() == MAX_REQS_PER_MINUTE) {
+			while (dtQueue.size() > 0
+				&& Duration.between(dtQueue.peek(), req.dt).getSeconds() > SECONDS_PER_MINUTE) {
+					dtQueue.poll();
+			}
+		}
+		if (dtQueue.size() < MAX_REQS_PER_MINUTE) {
+			dtQueue.add(req.dt);
+			return true;
+		} else {
+			return false;
+		}
+	}
+
+	// PRIVATE
+	// TEST ONLY
+	private static LocalDateTime makeTestTime(int minutes, int seconds) {
+		return LocalDateTime.of(2022, Month.MAY, 10, 10, minutes, seconds);
+	}
+
+	// Request
+	static class Request {
+		public LocalDateTime dt;
+		public Request() {
+			this.dt = LocalDateTime.now();
+		}
+
+		// TESTING ONLY
+		private Request(LocalDateTime dt) {
+			this.dt = dt;
+		}
+	}
+}

Tester.java

@@ -81,6 +81,14 @@ public void booleanEquals(boolean expected, boolean actual, String testTitle) {
         }
     }
 
+    public void isTrue(boolean actual, String testTitle) {
+        booleanEquals(true, actual, testTitle);
+    }
+
+    public void isFalse(boolean actual, String testTitle) {
+        booleanEquals(false, actual, testTitle);
+    }
+
     public void listNodeEquals(ListNode expected, ListNode actual, String testTitle) {
         if (expected == actual) {
             printTestSuccess(testTitle);