Bellman-Ford算法解决单源最短路问题

Posted 2020-08-22

 

#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
#define max 100
#define INF 999
struct edge{
    int u;
    int v;
    int w;
}e[max];
int vertex_num,edge_num;
int d[max];
void relax(int u,int v,int w){
    if(d[v]>d[u]+w)d[v]=d[u]+w;
}
bool Bellman_Ford(int s){
    int i,j;
    
    //Part 1:init 
    for(i=0;i<vertex_num;i++){
        d[i]=INF;
    }
    d[s]=0;
    
    //Part 2:relax
    for(i=0;i<vertex_num;i++){
        for(j=0;j<edge_num;j++){
            relax(e[j].u,e[j].v,e[j].w);
        }
    }
    
    //Part 3:determine whether there exist a negative cirlce
    for(i=0;i<edge_num;i++){
        if(d[e[i].u]>d[e[i].v]+e[i].w)return false;
    }
    return true;
}
int main(){
    int i,j;
    FILE *fin  = fopen ("dij.in", "r");
    FILE *fout = fopen ("dij.out", "w");
    
    char buf[10];
    fgets(buf,10,fin);
    edge_num=atoi(buf);
    printf("edge_num:%d\n",edge_num);
    
    fgets(buf,10,fin);
    vertex_num=atoi(buf);
    printf("vertex_num:%d\n",vertex_num);
    
    for(i=0;i<edge_num;i++){
        int start,end,weight;//start point,end point and the weight of edge
        fgets(buf,10,fin);
        sscanf(buf,"%d %d %d",&e[i].u,&e[i].v,&e[i].w);
        printf("start:%d end:%d weight:%d\n",e[i].u,e[i].v,e[i].w);
    }
    
    Bellman_Ford(0);
    for(i=0;i<vertex_num;i++){
        printf("%d ",d[i]);
    }
    return 0;
}