单源最短路（Bellman_Ford)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#define INF 0x7fffffff
using namespace std;

const int maxn = 1000;
const int maxm = 1000000;

typedef struct node{
    int w;
    int to;
    int next;
}NODE;

int dist[maxn];
NODE edge[maxm];
int head[maxn];
int num = 0;
int s = 0;
int n, m;

int Bellman_Ford(){
    int i, j, k;
    for(i = 0; i < n; i++){
        dist[i] = INF;
    }
    dist[s] = 0;//别忘了给S赋值这可是程序执行的开始。
    for(i= 0; i < n-1; i++){
        for(j = 0; j < n; j++){
            if(dist[j] == INF) { continue; }
            for(k = head[j]; k != -1; k = edge[k].next){
                if(edge[k].w != INF && dist[edge[k].to] > dist[j] + edge[k].w){
                    dist[edge[k].to] = dist[j] + edge[k].w;
                }
            }
        }
    }
    for(j = 0; j < n; j++){
        if(dist[j] == INF){ continue; }
        for(k = head[j]; k != -1; k = edge[k].next){
            if(edge[k].w !=INF && dist[edge[k].to] > dist[j] + edge[k].w){
                return false;
            }
        }
    }
    return true;
}

void output_result(){
    for(int i = 1; i <= n; i++){
        printf("%d\n", dist[i]);
    }
}

void init(){
    num = 0;
    memset(dist, 0, sizeof(dist));
    memset(head, -1, sizeof(head));
}

int main()
{
    int a = 0, b = 0, c = 0;
    while(scanf("%d%d", &n, &m)!=EOF){
        init();
        a = INF;
        cout << a << endl;
        for(int i = 0; i < m; i++){
            scanf("%d%d%d", &a, &b, &c);
            edge[num].w = c;
            edge[num].to = b;
            edge[num].next = head[a];
            head[a] = num;
            num++;
        }
        cout << "please input a source:" << endl;
        scanf("%d", &s);
        int  res = Bellman_Ford();
        if(res) {
            output_result();
        }
    }
        return 0;
}
/****************
测试数据算法导论P362
5 10
1 2 6
1 3 7
2 3 8
2 4 5
2 5 -4
3 4 -3
3 5 9
4 2 -2
5 4 7
5 1 2
************/