Pairwise Linked List Swap - Amazon Top Interview Questions


Problem Statement :


Given a singly linked list node, swap each pair of nodes and return the new head.

Constraints

n ≤ 100,000 where n is the number of nodes in node

Example 1

Input

node = [0, 1, 3, 4]

Output

[1, 0, 4, 3]

Example 2

Input

node = [1, 2, 3]

Output

[2, 1, 3]


Solution :



title-img 




                        Solution in C++ :

/**
 * class LLNode {
 *     public:
 *         int val;
 *         LLNode *next;
 * };
 */
LLNode* solve(LLNode* node) {
    if (!node) return node;
    // LLNode* hd=node;
    LLNode* tmp = node;
    if (node && node->next) {
        tmp = node->next;
        node->next = node->next->next;
        tmp->next = node;
        node->next = solve(tmp->next->next);
    }

    return tmp;
}
                    




                        Solution in Python : 
                            
# class LLNode:
#     def __init__(self, val, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def solve(self, node):
        if not node or not node.next:
            return node

        tail = self.solve(node.next.next)

        head = node.next
        head.next = node
        node.next = tail

        return head


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