# Delete continuous nodes with sum K from a given linked list

Given a singly linked list and an integer K, the task is to remove all the continuous set of nodes whose sum is K from the given linked list. Print the updated linked list after the removal. If no such deletion can occur, print the original Linked list.

Examples:

Input: Linked List: 1 -> 2 -> -3 -> 3 -> 1, K = 3
Output: -3 -> 1
Explanataion:
The nodes with continuous sum 3 are:
1) 1 -> 2
2) 3
Therefore, after removing these chain of nodes Linked List becomes: -3-> 1

Input: Linked List: 1 -> 1 -> -3 -> -3 -> -2, K = 5
Output: 1 -> 1 -> -3 -> -3 -> -2
Explanataion:
No continuous nodes exits with sum K

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

1. Append Node with value zero at the starting of the linked list.
2. Traverse the given linked list.
3. During traversal store the sum of the node value till that node with the reference of the current node in an unordered_map.
4. If there is Node with value (sum – K) present in the unordered_map then delete all the nodes from the node corresponding to value (sum – K) stored in map to the current node and update the sum as 0.
5. If there is no Node with value (sum – K) present in the unordered_map, then stored the current sum with node in the map.

Below is the implementation of the above approach:

 `// C++ program for the above approach ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// A Linked List Node ` `struct` `ListNode { ` `    ``int` `val; ` `    ``ListNode* next; ` ` `  `    ``// Contructor ` `    ``ListNode(``int` `x) ` `        ``: val(x), next(NULL) ` `    ``{ ` `    ``} ` `}; ` ` `  `// Function to create Node ` `ListNode* getNode(``int` `data) ` `{ ` `    ``ListNode* temp; ` `    ``temp = (ListNode*)``malloc``(``sizeof``(ListNode)); ` `    ``temp->val = data; ` `    ``temp->next = NULL; ` `    ``return` `temp; ` `} ` ` `  `// Function to print the Linked List ` `void` `printList(ListNode* head) ` `{ ` `    ``while` `(head->next) { ` `        ``cout << head->val << ``" -> "``; ` `        ``head = head->next; ` `    ``} ` `    ``printf``(``"%d"``, head->val); ` `} ` ` `  `// Function that removes continuos nodes ` `// whose sum is K ` `ListNode* removeZeroSum(ListNode* head, ` `                        ``int` `K) ` `{ ` `    ``// Root node initialise to 0 ` `    ``ListNode* root = ``new` `ListNode(0); ` ` `  `    ``// Append at the front of the given ` `    ``// Linked List ` `    ``root->next = head; ` ` `  `    ``// Map to store the sum and reference ` `    ``// of the Node ` `    ``unordered_map<``int``, ListNode*> umap; ` ` `  `    ``umap[0] = root; ` ` `  `    ``// To store the sum while traversing ` `    ``int` `sum = 0; ` ` `  `    ``// Traversing the Linked List ` `    ``while` `(head != NULL) { ` ` `  `        ``// Find sum ` `        ``sum += head->val; ` ` `  `        ``// If found value with (sum - K) ` `        ``if` `(umap.find(sum - K) != umap.end()) { ` ` `  `            ``ListNode* prev = umap[sum - K]; ` `            ``ListNode* start = prev; ` ` `  `            ``// Delete all the node ` `            ``// traverse till current node ` `            ``int` `aux = sum; ` ` `  `            ``// Traverse till current head ` `            ``while` `(prev != head) { ` `                ``prev = prev->next; ` `                ``aux += prev->val; ` `                ``if` `(prev != head) { ` `                    ``umap.erase(aux); ` `                ``} ` `            ``} ` ` `  `            ``// Update the start value to ` `            ``// the next value of current head ` `            ``start->next = head->next; ` ` `  `            ``// Update sum to zero ` `            ``sum = 0; ` `        ``} ` ` `  `        ``// If (sum - K) value not found ` `        ``else` `{ ` `            ``umap[sum] = head; ` `        ``} ` ` `  `        ``head = head->next; ` `    ``} ` ` `  `    ``// Return the value of updated ` `    ``// head node ` `    ``return` `root->next; ` `} ` ` `  `// Driver Code ` `int` `main() ` `{ ` `    ``// head Node ` `    ``ListNode* head; ` ` `  `    ``// Create Linked List ` `    ``head = getNode(1); ` `    ``head->next = getNode(2); ` `    ``head->next->next = getNode(-3); ` `    ``head->next->next->next = getNode(3); ` `    ``head->next->next->next->next = getNode(1); ` ` `  `    ``// Given sum K ` `    ``int` `K = 5; ` ` `  `    ``// Function call to get head node ` `    ``// of the updated Linked List ` `    ``head = removeZeroSum(head, K); ` ` `  `    ``// Print the updated Linked List ` `    ``printList(head); ` `    ``return` `0; ` `} `

Output:

```1 -> 2 -> -3 -> 3 -> 1
```

Time Complexity: O(N), where N is the number of Node in the Linked List.
Auxiliary Space Complexity: O(N), where N is the number of Node in the Linked List.

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