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
************/