Day-22 Swap of linkedlist nodes without swapping data

Author: mandliya

linked_list_problems/swapNodesWithoutSwappingData.cpp

@@ -0,0 +1,105 @@
+/*
+ * Problem : Given a linked list, and two data values, x and y. 
+ * Goal:     Swap the nodes of linkedlist by swapping pointers ( and not swapping data) such that nodes with data x will contain y and vice versa.
+ *
+ */
+
+
+#include <iostream>
+
+
+struct Node {
+  int data;
+  Node* next;
+  Node(int d) : data{d}, next{nullptr} { }
+};
+
+
+/**** Algorithm Function ****/
+void swapSpecial(Node* & head, int x, int y) {
+
+  //empty list
+  if (head == nullptr) {
+    return;
+  }
+
+  //nothing to do if both are values are same.
+  if ( x == y ) {
+    return;
+  }
+
+  Node * prevx = nullptr;
+  Node * currx = head;
+  Node * prevy = nullptr;
+  Node * curry = head;
+
+  //search for x
+  while ( currx && currx->data != x ) {
+    prevx = currx;
+    currx = currx->next;
+  }
+  //search for y
+  while ( curry && curry->data != y ) {
+    prevy = curry;
+    curry = curry->next;
+  }
+  //x or y not found
+  if ( currx == nullptr || curry == nullptr ) {
+    return;
+  }
+
+  //if x is not head
+  if ( prevx != nullptr ) {
+    prevx->next = curry;
+  } else {
+    head = curry;
+  }
+
+  //similarly if y is not head
+  if ( prevy != nullptr) {
+    prevy->next = currx;
+  } else {
+    head = curry;
+  }
+
+  //now lets swap the next pointers
+  Node *temp = curry->next;
+  curry->next = currx->next;
+  currx->next = temp;
+}
+
+void insert(Node* & head, int data) {
+  if (head == nullptr) {
+    head = new Node(data);
+    return;
+  }
+  Node *temp = head;
+  while(temp->next != nullptr) {
+    temp = temp->next;
+  }
+  temp->next = new Node(data);
+}
+
+void printList(Node * head) {
+  while (head) {
+    std::cout << head->data << "-->";
+    head = head->next;
+  }
+  std::cout << "null" << std::endl;
+}
+
+int main() {
+  Node *head = nullptr;
+  insert(head, 10);
+  insert(head, 15);
+  insert(head, 12);
+  insert(head, 13);
+  insert(head, 20);
+  insert(head, 14);
+  printList(head);
+  std::cout << "Replacing 12 with 20 and 20 with 12:\n";
+  swapSpecial(head, 12, 20);
+  printList(head);
+
+  return 0;
+}