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TortoiseAndHare.java

@@ -0,0 +1,79 @@
+class Node {
+	int  data;
+	Node next;
+
+	Node(int d) {
+		this.data = d;
+		this.next = null;
+	}
+}
+
+public class TortoiseAndHare {
+	public Node head = null;
+	public Node last;
+	Node        slow_p, fast_p;
+	int         startingIndex, endingIndex;
+	public void push(int new_data) {
+		Node new_node = new Node(new_data);
+		if (this.head == null) {
+			this.last = new_node;
+		}
+		new_node.next = this.head;
+		this.head = new_node;
+	}
+
+	private boolean detectLoop() {
+		this.slow_p = this.head;
+		this.fast_p = this.head;
+		while ((this.slow_p != null) && (this.fast_p != null) && (this.fast_p.next != null)) {
+			this.slow_p = this.slow_p.next;
+			this.fast_p = this.fast_p.next.next;
+			if (this.slow_p == this.fast_p) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	public static void main(String args[]) {
+		TortoiseAndHare llist = new TortoiseAndHare();
+
+		llist.push(1);
+		llist.push(2);
+		llist.push(3);
+		llist.push(4);
+		llist.push(5);
+		llist.push(6);
+		llist.push(7);
+
+		llist.head.next.next.next.next.next = llist.head.next;
+
+		if(llist.detectLoop()) {
+			System.out.println("Loop Detected");
+			llist.findStartOfLoop();
+			llist.findEndOfLoop();
+			System.out.println("Starting index of loop:" + llist.startingIndex);
+			System.out.println("Ending index of loop:" + llist.endingIndex);
+		}
+	}
+
+	private void findEndOfLoop() {
+		this.fast_p        = this.slow_p.next;
+		this.endingIndex   = this.startingIndex + 1;
+		while (this.slow_p != this.fast_p) {
+			this.endingIndex++;
+			this.fast_p = this.fast_p.next;
+		}
+		this.endingIndex--;
+	}
+
+	private void findStartOfLoop() {
+		this.slow_p = this.head;
+		this.startingIndex = 0;
+		while (this.slow_p != this.fast_p) {
+			this.startingIndex++;
+			this.slow_p = this.slow_p.next;
+			this.fast_p = this.fast_p.next;
+		}
+	}
+}