问题重述

Problem Statement：

Given a linked list, swap the two nodes present at position i and j. The positions are based on 0-based indexing.

Note: You have to swap the nodes and not just the values.

Example: * linked_list = 3 4 5 2 6 1 9 * positions = 3 4 * output = 3 4 5 6 2 1 9

Explanation: * The node at position 3 has the value 2 * The node at position 4 has the value 6 * Swapping these nodes will result in a final order of nodes of 3 4 5 6 2 1 9

python实现

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class Node:
    """LinkedListNode class to be used for this problem"""
    def __init__(self, data):
        self.value = data
        self.next = None

def swap_nodes(head, left_index, right_index):
    i = 0
    node = head
    left_node = head
    left_value = None
    right_node = head
    right_value = None
    while i <= right_index:
        if i == left_index:
            left_node = node
            left_value = node.value
        if i == right_index:
            right_node = node
            right_value = node.value
        i += 1
        node = node.next
    left_node.value = right_value
    right_node.value = left_value
    return head

测试用例： 

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# helper functions for testing purpose
def create_linked_list(arr):
    if len(arr)==0:
        return None
    head = Node(arr[0])
    tail = head
    for data in arr[1:]:
        tail.next = Node(data)
        tail = tail.next
    return head

def print_linked_list(head):
    while head:
        print(head.value, end=" ")
        head = head.next
    print()

arr = [3, 4, 5, 2, 6, 1, 9]
head = create_linked_list(arr)
left_index = 3
right_index = 4
print_linked_list(swap_nodes(head, left_index, right_index))

arr = [3, 4, 5, 2, 6, 1, 9]
left_index = 2 
right_index = 4
head = create_linked_list(arr)
print_linked_list(swap_nodes(head, left_index, right_index))

arr = [3, 4, 5, 2, 6, 1, 9]
left_index = 0
right_index = 1
head = create_linked_list(arr)
print_linked_list(swap_nodes(head, left_index, right_index))