文本文件中的 BellmanFord 未提供与手动输入相同的输出

Question

我正在尝试从文本文件中读取权重，但它没有提供与我手动设置它们时相同的输出。这是 adjlist.txt 文件中的数据：

现在当我在没有读取机制的情况下手动设置这些时，例如： graph->edge[0].weight = 5 等等它给了我这个输出

Vertex   Distance from Source
0        0
1        6
2        10
3        7
4        10

我试过仅通过打印来获取数据，它确实可以正确读取数据，但无法正确解析数据 "cout << s[0] << "\n";"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include<bits/stdc++.h>
#include<fstream>
#include<string>

using namespace std;
// a structure to represent a weighted edge in graph
struct Edge
{
        int src, dest, weight;
};

// a structure to represent a connected, directed and weighted graph
struct Graph
{
        // V-> Number of vertices, E-> Number of edges
        int V, E;

        // graph is represented as an array of edges.
        struct Edge* edge;
};

// Creates a graph with V vertices and E edges
struct Graph* createGraph(int V, int E)
{
    struct Graph* graph = (struct Graph*) malloc(sizeof(struct Graph));
    graph->V = V;
    graph->E = E;

    graph->edge = (struct Edge*) malloc(graph->E * sizeof(struct Edge));

    return graph;
}

// A utility function used to print the solution
void printArr(int dist[], int n)
{
    printf("Vertex   Distance from Source\n");
    for (int i = 0; i < n; ++i)
        printf("%d \t\t %d\n", i, dist[i]);
}
void relax(struct Graph* graph, int V, int dist[], int E, int src)
{
    for (int i = 1; i <= V - 1; i++)
    {
        for (int j = 0; j < E; j++)
        {
            int u = graph->edge[j].src;
            int v = graph->edge[j].dest;
            int weight = graph->edge[j].weight;
            if (dist[u] != INT_MAX && dist[u] + weight < dist[v])
                dist[v] = dist[u] + weight;
        }
    } 
}

 void int_source(int V,int dist[],int E,int src)
 {
       for (int i = 0; i < V; i++)
        dist[i] = INT_MAX;
    dist[src] = 0;
 }

void negweight(struct Graph* graph, int V, int dist[], int E, int src)
{
    for (int i = 0; i < E; i++)
    {
        int u = graph->edge[i].src;
        int v = graph->edge[i].dest;
        int weight = graph->edge[i].weight;
        if (dist[u] != INT_MAX && dist[u] + weight < dist[v])
            printf("Graph contains negative weight cycle");
    }
}
// The main function that finds shortest distances from src to all other
// vertices using Bellman-Ford algorithm.  The function also detects negative
// weight cycle
void BellmanFord(struct Graph* graph, int src)
{
    int V = graph->V;
    int E = graph->E;
    int dist[V];
    int_source(V,dist,E,src);
    relax(graph,V,dist,E,src);
    negweight(graph,V,dist,E,src);
    printArr(dist, V);
    return;
}

int main()
{
    int V = 5; // Number of vertices in graph
    int E = 10; // Number of edges in graph
    struct Graph* graph = createGraph(V, E);

    string s;
cout << "Your input file contains this adjacency list\n";
ifstream infile("adjlist.txt");
while(getline(infile,s))
{
    graph->edge[0].src = 1;
    graph->edge[0].dest = 2;
    graph->edge[0].weight = s[0]-'0';

    // add edge 0-2 (or A-C in above figure)
    graph->edge[1].src = 1;
    graph->edge[1].dest = 3;
    graph->edge[1].weight = s[0]-'0';

    // add edge 1-2 (or B-C in above figure)
    graph->edge[2].src = 1;
    graph->edge[2].dest = 4;
    graph->edge[2].weight = s[0]-'0';

    // add edge 1-3 (or B-D in above figure)
    graph->edge[3].src = 2;
    graph->edge[3].dest = 1;
    graph->edge[3].weight = s[0]-'0';

    // add edge 1-4 (or A-E in above figure)
    graph->edge[4].src = 3;
    graph->edge[4].dest = 2;
    graph->edge[4].weight = s[0]-'0';

    // add edge 3-2 (or D-C in above figure)
    graph->edge[5].src = 3;
    graph->edge[5].dest = 4;
    graph->edge[5].weight = s[0]-'0';

    // add edge 3-1 (or D-B in above figure)
    graph->edge[6].src = 4;
    graph->edge[6].dest = 2;
    graph->edge[6].weight = s[0]-'0';

    // add edge 4-3 (or E-D in above figure)
    graph->edge[7].src = 4;
    graph->edge[7].dest = 0;
    graph->edge[7].weight = s[0]-'0';
     // add edge 4-3 (or E-D in above figure)
    graph->edge[8].src = 0;
    graph->edge[8].dest = 1;
    graph->edge[8].weight = s[0]-'0';    // add edge 4-3 (or E-D in above figure)

    graph->edge[9].src = 0;
    graph->edge[9].dest = 3;
    graph->edge[9].weight = s[0]-'0';
}
    BellmanFord(graph, 0);

    return 0;
} `

预期结果应该是

Vertex   Distance from Source
0        0
1        6
2        10
3        7
4        10

我得到的结果是

Vertex   Distance from Source
0        0
1        7
2        14
3        7
4        14

Answer 1

仔细看看主要的解析循环。对于从文件中读取的每一行，它为所有节点设置相同的权重值。

示例：

graph->edge[0].src = 1;
graph->edge[0].dest = 2;
graph->edge[0].weight = s[0]-'0'; // 5

// add edge 0-2 (or A-C in above figure)
graph->edge[1].src = 1;
graph->edge[1].dest = 3;
graph->edge[1].weight = s[0]-'0'; // still five.

你要的是

int index = 0;
while(getline(infile,s))
{
    graph->edge[index].src = 1;
    graph->edge[index].dest = 2;
    graph->edge[index].weight = s[0]-'0';
    index++
}

不幸的是，这似乎并不能解决所有问题。我看不到输入

的 body 的方法

if (dist[u] != INT_MAX && dist[u] + weight < dist[v])

使用给定的输入。

Answer 2

所以问题的答案是在@user4581301 的帮助下得到的我更改了我的输入文件，因此源和目标也将添加到文件中。现在循环运行正常

1,2,5
1,3,8
1,4,4
2,1,2
3,2,3
3,4,9
4,2,7
4,0,2
0,1,6
0,3,7

这是我所做的编辑

 int index = 0;

while(getline(infile,s))
{
    graph->edge[index].src = s[0]-'0';
    graph->edge[index].dest = s[2]-'0';
    graph->edge[index].weight = s[4]-'0';
    index++;
}

文本文件中的 BellmanFord 未提供与手动输入相同的输出

BellmanFord from text file not giving the same output as manual input

c++

algorithm

data-structures

readfile

bellman-ford