Create detect_loop.cpp

detect_loop.cpp

@@ -0,0 +1,59 @@
+// C++ program to detect loop in a linked list
+// using hashset
+#include <bits/stdc++.h>
+using namespace std;
+
+class Node {
+public:
+    int data;
+    Node* next;
+    Node(int x) {
+        this->data = x;
+        this->next = nullptr;
+    }
+};
+
+// Function that returns true if there is a loop in linked
+// list else returns false.
+bool detectLoop(Node* head) {
+    unordered_set<Node*>st;
+
+    // loop that runs till the head is nullptr
+    while (head != nullptr) {
+
+        // If this node is already present
+        // in hashmap it means there is a cycle
+        // (Because you will be encountering the
+        // node for the second time).
+        if (st.find(head) != st.end())
+            return true;
+
+        // If we are seeing the node for
+        // the first time, insert it in hash
+        st.insert(head);
+
+        head = head->next;
+    }
+    return false;
+}
+
+int main() {
+
+    // Create a hard-coded linked list:
+    // 10 -> 20 -> 30 -> 40 -> 50 -> 60
+    Node* head = new Node(10);
+    head->next = new Node(20);
+    head->next->next = new Node(30);
+    head->next->next->next = new Node(40);
+    head->next->next->next->next = new Node(50);
+    head->next->next->next->next->next = new Node(60);
+
+    head->next->next->next->next = head;
+
+    if (detectLoop(head))
+        cout << "true";
+    else
+        cout << "false";
+
+    return 0;
+}