题目

Given a constant K and a singly linked list L, you are supposed to reverse the links of every K elements on L. For example, given L being 1→2→3→4→5→6, if K=3K = 3K=3, then you must output 3→2→1→6→5→4; if K=4K = 4K=4, you must output 4→3→2→1→5→6.

Input Specification:

Each input file contains one test case. For each case, the first line contains the address of the first node, a positive N(≤$10^{5}$​​) which is the total number of nodes, and a positive K (≤N) which is the length of the sublist to be reversed. The address of a node is a 5-digit nonnegative integer, and NULL is represented by -1.
Then N lines follow, each describes a node in the format:

Address Data Next

where Address is the position of the node, Data is an integer, and Next is the position of the next node.

Output Specification:

For each case, output the resulting ordered linked list. Each node occupies a line, and is printed in the same format as in the input.

Sample Input:

00100 6 4 
00000 4 99999
00100 1 12309
68237 6 -1
99999 5 68237
12309 2 33218

Sample Output:

00000 4 33218 
33218 3 12309 
12309 2 00100 
00100 1 99999 
99999 5 68237 
68237 6 -1

注意

  • supposed to reverse the links of every K elements on L(反转每k个数)

  • The address of a node is a 5-digit nonnegative integer, and NULL is represented by -1

解法1:利用空间换时间

  1. 定义一个长10000数组,下标表示每行的Address值。

  2. 根据结点的顺序,依次加入到一个vector中。

  3. 对vector中的每个K元素进行反转。

  4. 输出最终结果

#include <iostream>
#include <vector>
using namespace std;

#define MAX_ADDRESS_SIZE 100000

struct Node
{
    int Address = -1;
    int Data = 0;
    int Next = -1;
};

void reverse_linked_nodes(vector<Node>& list, int start, int end)
{
    while (start < end)
    {
        Node temp = list[start];
        list[start] = list[end];
        list[end] = temp;
        start++;
        end--;
    }
}

int main()
{
    // read first command line
    int head_addr, node_count, reverse_node_count;
    cin >> head_addr >> node_count >> reverse_node_count;

    // read list nodes
    vector<Node> nodes(MAX_ADDRESS_SIZE);
    for (int i = 0; i < node_count; i++)
    {
        int addr, data, next;
        cin >> addr >> data >> next;
        nodes[addr].Address = addr;
        nodes[addr].Data = data;
        nodes[addr].Next = next;
    }

    // insert to vector with sorted
    vector<Node> node_list;
    node_list.push_back(nodes[head_addr]);  // push the first node
    while (node_list.back().Next != -1)
    {
        node_list.push_back(nodes[node_list.back().Next]); //push the next node
    }

    // reverse every reverse_count elements of real link list
    int reverse_times = node_list.size() / reverse_node_count;
    for (int i = 0; i < reverse_times; i++)
    {
        int start = i * reverse_node_count;
        int end = start + reverse_node_count -1;
        reverse_linked_nodes(node_list, start, end);
    }

    // output result
    for (int i = 0; i < node_list.size()-1; i++)
    {
        printf("%05d %d %05dn", node_list[i].Address, node_list[i].Data, node_list[i+1].Address);
    }
    printf("%05d %d %dn", node_list.back().Address, node_list.back().Data, -1);

    return 0;
}

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