sort array with 0,1,2

A-Array/sort_array.cpp

@@ -0,0 +1,59 @@
+// C++ program to sort an array
+// with 0, 1 and 2 in a single pass
+#include <bits/stdc++.h>
+using namespace std;
+
+// Function to sort the input array,
+// the array is assumed
+// to have values in {0, 1, 2}
+void sort012(int a[], int arr_size)
+{
+	int lo = 0;
+	int hi = arr_size - 1;
+	int mid = 0;
+
+	// Iterate till all the elements
+	// are sorted
+	while (mid <= hi) {
+		switch (a[mid]) {
+
+		// If the element is 0
+		case 0:
+			swap(a[lo++], a[mid++]);
+			break;
+
+		// If the element is 1 .
+		case 1:
+			mid++;
+			break;
+
+		// If the element is 2
+		case 2:
+			swap(a[mid], a[hi--]);
+			break;
+		}
+	}
+}
+
+// Function to print array arr[]
+void printArray(int arr[], int arr_size)
+{
+	// Iterate and print every element
+	for (int i = 0; i < arr_size; i++)
+		cout << arr[i] << " ";
+}
+
+
+int main()
+{
+	int arr[] = { 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1 };
+	int n = sizeof(arr) / sizeof(arr[0]);
+
+	sort012(arr, n);
+
+	cout << "array after segregation ";
+
+	printArray(arr, n);
+
+	return 0;
+}

L-LinkedList/swap_nodes.cpp

@@ -0,0 +1,119 @@
+/*
+    You are given the head of a linked list, and an integer k.
+
+    Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed).
+*/
+#include<bits/stdc++.h>
+using namespace std;
+
+struct ListNode {
+      ListNode *next;
+      int val;
+      ListNode() : val(0), next(nullptr) {}
+      ListNode(int x) : val(x), next(nullptr) {}
+      ListNode(int x, ListNode *next) : val(x), next(next) {}
+  };
+
+    ListNode* swapNodes(ListNode* head, int k) {
+        // repositioning head
+        head = new ListNode(-1, head);
+        // support variables
+        ListNode *prev1 = head, *prev2 = head, *curr = head;
+        // finding prev1
+        while (--k) {
+            prev1 = prev1->next;
+            curr = curr->next;
+        }
+        curr = curr->next;
+        // finding prev2
+        while (curr->next) {
+            prev2 = prev2->next;
+            curr = curr->next;
+        }
+        // switching nodes, with n1 = prev1->next and n2 = prev2->next:
+        // edge case: n1->next = n2
+        if (prev1->next == prev2) {
+            // storing n2 in curr
+            curr = prev2->next;
+            // attaching n2->next right after n1
+            prev1->next->next = prev2->next->next;
+            // attaching n1 after n2
+            curr->next = prev1->next;
+            // attaching n2 to prev1
+            prev1->next = curr;
+            return head->next;
+        }
+        // storing n1 in curr
+        curr = prev1->next;
+        // attaching n2 right after prev1
+        prev1->next = prev2->next;
+        // since prev1 is no longer needed, we will use it to store next2 = n2->next
+        prev1 = prev2->next->next;
+        // finishing splicing n2 in place
+        prev2->next->next = curr->next;
+        // adding n1 after prev2
+        prev2->next = curr;
+        // connecting n2->next riht after n1
+        curr->next = prev1;
+
+    }
+
+
+/* Function to insertAtBeginning a node */
+void insertAtBeginning(struct ListNode** head, int dataToBeInserted)
+{
+    struct ListNode* curr = new ListNode;
+    curr->val = dataToBeInserted;
+    curr->next = NULL;    
+    if(*head == NULL)
+            *head=curr; //If this is first node make this as head of list
+
+    else
+        {
+            curr->next=*head; //else make the curr (new) node's next point to head and make this new node a the head
+            *head=curr;
+        }
+
+        //O(1) constant time
+}
+
+//display linked list
+void display(struct ListNode**node)
+{
+    struct ListNode *temp= *node;
+    while(temp!=NULL)
+        {
+            if(temp->next!=NULL)
+            cout<<temp->val<<"->";
+            else
+            cout<<temp->val;
+
+            temp=temp->next; //move to next node
+        }
+        //O(number of nodes)
+    cout<<endl;
+}
+
+
+int main()
+{
+    struct ListNode* head =NULL;
+    insertAtBeginning(&head, 9);
+    insertAtBeginning(&head, 8);
+    insertAtBeginning(&head, 7);
+    insertAtBeginning(&head, 6);
+    insertAtBeginning(&head, 5);
+    insertAtBeginning(&head, 4);
+    insertAtBeginning(&head, 3);
+    insertAtBeginning(&head, 2);
+    insertAtBeginning(&head, 1);
+
+
+    cout<<"Input linked list is: ";
+    display(&head);
+    int x = 2;
+    swapNodes(head,x);
+    cout<<"output LL after swapping "<<x<<" and is: ";
+    display(&head);
+
+}