时间戳

首页 > 解决方案 > 在 for 循环中索引向量

c++ - 在 for 循环中索引向量

问题描述

这是Returning name of最低节点的后续，只是现在有了更多的进展和更少的错误。

和上次一样，这是针对大学课程的，所以复制粘贴对我来说并不是最有利的，即使它确实有效。

我现在遇到的问题与 LeastDistance 函数中向量的索引有关，因为当代码在调试器内外运行时会生成运行时异常，并显示向量下标超出范围的消息。如果有人比我更熟悉向量库，相关行是 1804。这是在同一个函数中访问 for 循环时触发的。

for (int j = 0; j < hnode[i].nodes.size(); j++)

到目前为止，我已经编写了一个小的帮助函数 GetIndex，但我不确定它的代码是否正确，以及如何在 LeastDistance 函数本身中实现它。下面是完整的代码（为粗制滥造的格式道歉，这里的编辑让我有些悲伤）。

#include "stdafx.h"
#include<iostream>
#include<vector>
#define INF = 9999;

using namespace std;

struct Node
{
    char nodeLink;  //adjacent link
    int cost;       //cost of a link
};                  //to use in Dijkstra algorithm


class HeadNode
{
public:
    char Name;
    bool Visited;
    vector<Node> nodes;
    HeadNode(char x) { Name = x; Visited = false; }

};

class Graph
{
    char Start = 'A';
    char StartNode;
    char CurrentNode;
    char Destination;
    int TotalCost = 0;
    vector<HeadNode> hnode;
    vector<char> path;
    vector<int> weight;

public:
    Graph();
    void createHeadNode(char X);
    void createAdjMatrix();
    char LeastDistance(char node);
    void printAdjMatrix();
    void Dijkstra(char StartNode, char Destination);
    void DestinationChangeCaller();
    char GetStartNode();
    int GetIndex(char CurrentNode);
};



int main()
{
    Graph graph;
    graph.createHeadNode('A');
    graph.createHeadNode('B');
    graph.createHeadNode('C');
    graph.createHeadNode('D');
    graph.createHeadNode('E');
    graph.createAdjMatrix();
    graph.GetStartNode();
    graph.DestinationChangeCaller();

    system("pause");
    return 0;
}

void Graph::DestinationChangeCaller()
{
    for (Destination = 'A'; Destination <= 'E'; Destination++)
    {
        Dijkstra(StartNode, Destination);
    }
}



Graph::Graph()
{
}

int Graph::GetIndex(char node)
{
    return(node - 'A');
}

void Graph::createHeadNode(char x)
{
    hnode.push_back(x);
}

char Graph::GetStartNode() // elementary get function with no error correction.
{
    char got;
    cout << "Please enter a node from A-E to start from:  ";
    cin >> got;
    cout << endl;
    return got;
}

void Graph::createAdjMatrix()
{
    hnode[0].nodes.push_back({ 'B', 4 });
    hnode[0].nodes.push_back({ 'C', 1 });
    hnode[1].nodes.push_back({ 'A', 4 });
    hnode[1].nodes.push_back({ 'C', 2 });
    hnode[1].nodes.push_back({ 'D', 1 });
    hnode[2].nodes.push_back({ 'A', 1 });
    hnode[2].nodes.push_back({ 'B', 2 });
    hnode[2].nodes.push_back({ 'D', 3 });
    hnode[2].nodes.push_back({ 'E', 1 });
    hnode[3].nodes.push_back({ 'B', 1 });
    hnode[3].nodes.push_back({ 'C', 3 });
    hnode[3].nodes.push_back({ 'E', 1 });
    hnode[4].nodes.push_back({ 'C', 1 });
    hnode[4].nodes.push_back({ 'D', 1 });

}

void Graph::printAdjMatrix()
{
    cout << "The adjacency list that represents the graph is :";
    for (int i = 0; i < hnode.size(); i++)
    {
        cout << endl;
        cout << hnode[i].Name << " -> ";

        for (int j = 0; j < hnode[i].nodes.size(); ++j)
        {
            cout << hnode[i].nodes[j].nodeLink << ", " << hnode[i].nodes[j].cost << ", ";
        }
    }

    cout << endl;
    cout << endl;
    cout << endl;

    for (int i = 0; i < hnode.size(); i++)
    {
        cout << "Shortest distance from node " << Start << " to node " << hnode[i].Name << " is:" << weight[i] << endl;
        cout << "Shortest path is : ";

        for (int j = 0; j < path.size(); j++)
        {
            cout << path[j] << endl;
        }
    }
}

char Graph::LeastDistance(char node)
{
    int smallest = 9999;
    char smallestNode = node;
    int idx = 0;
    int i = GetIndex(node);

    for (int j = 0; j < hnode[i].nodes.size(); j++)
    {
        if ((node == hnode[i].Name) && (hnode[i].nodes[j].cost <= smallest) && (hnode[i].Visited == false))
        {
            smallest = hnode[i].nodes[j].cost;
            smallestNode = hnode[i].nodes[j].nodeLink;
            idx = i;
        }

    }
    hnode[idx].Visited = true;
    TotalCost = TotalCost + smallest;
    return(smallestNode);
}

void Graph::Dijkstra(char StartNode, char Destination)
{
    CurrentNode = StartNode;
    if (CurrentNode == Destination)
    {
        cout << "the start is the destination, therefore the cost will be 0." << endl;
    }
    else
    {
        cout << StartNode << "->";
        while (true)
        {
            if (CurrentNode != Destination)
            {
                CurrentNode = LeastDistance(CurrentNode);
                cout << CurrentNode << "->";
            }
            else if (CurrentNode == Destination)
            {
                cout << endl;
                cout << "The total cost of this path is:" << TotalCost;
                cout << endl;
                TotalCost = 0;//reset cost
                break;
            }
        }
    }
}

编辑：我从顶部更改了以下几行，错误已修复，但输出仍不符合预期。

class Graph
{
    char Start;
    char StartNode;
    char CurrentNode;
    char Destination;
    int TotalCost = 0;
    vector<HeadNode> hnode;
    vector<char> path;
    vector<int> weight;

public:
    Graph();
    void createHeadNode(char X);
    void createAdjMatrix();
    char LeastDistance(char node);
    void printAdjMatrix();
    void Dijkstra(char StartNode, char Destination);
    void DestinationChangeCaller(char Start);
    char GetStartNode();
    int GetIndex(char CurrentNode);
};



int main()
{
    Graph graph;
    graph.createHeadNode('A');
    graph.createHeadNode('B');
    graph.createHeadNode('C');
    graph.createHeadNode('D');
    graph.createHeadNode('E');
    graph.createAdjMatrix();
    graph.GetStartNode();
    graph.DestinationChangeCaller(graph.GetStartNode());

    system("pause");
    return 0;
}

void Graph::DestinationChangeCaller(char Start)
{
    for (Destination = 'A'; Destination <= 'E'; Destination++)
    {
        Dijkstra(Start, Destination);
    }
}

标签： c++vectorindexingdijkstra

解决方案

可能还有其他问题，但这里有一个：

char Graph::GetStartNode() // elementary get function with no error correction.
{
    char got;
    cout << "Please enter a node from A-E to start from:  ";
    cin >> got;
    cout << endl;
    return got;
}

因此 GetStartNode 返回用户输入。它不会更新成员变量 StartNode

当您调用 from 时，您不使用返回值main：

graph.createAdjMatrix();
graph.GetStartNode();    // <----- The return value isn't used
graph.DestinationChangeCaller();

所以在这里：

void Graph::DestinationChangeCaller()
{
    for (Destination = 'A'; Destination <= 'E'; Destination++)
    {
        Dijkstra(StartNode, Destination);
                 ^^^^^^^^^
    }
}

StartNode 未初始化。

推荐阅读