Day 47 算法笔记之提高篇（4）10.4.2 Bellman-Ford算法

#include<cstdio>
#include<vector>
#include<cstring>
#include<set>
#include<algorithm>
using namespace std;

const int maxv = 510;
const int inf = 1000000000;

struct node{
	int v,dis;
	node(int _v,int _dis) : v(_v),dis(_dis) {}
};

vector<node> adj[maxv];

int n,m,st,ed,weight[maxv];
int d[maxv],w[maxv],num[maxv];
set<int> pre[maxv];

void bellman(int s){
	fill(d,d+maxv,inf);
	memset(num,0,sizeof(num));
	memset(w,0,sizeof(w));
	d[s] = 0;
	w[s] = weight[s];
	num[s] = 1;
	
	for(int i=0;i<n-1;i++){
		for(int u=0;u<n;u++){
			for(int j=0;j<adj[u].size();j++){
				int v = adj[u][j].v;
				int dis=adj[u][j].dis;
				if(d[u]+dis<d[v]){
					d[v] = d[u] + dis;
					w[v] = w[u] + weight[v];
					num[v] = num[u];
					pre[v].clear();
					pre[v].insert(u);
				}else if(d[u]+dis==d[v]){
					if(w[u]+weight[v]>w[v]){
						w[v] = w[u] + weight[v];
					}
					pre[v].insert(u);
					num[v] = 0;
					set<int>::iterator it;
					for(it=pre[v].begin();it!=pre[v].end();it++){
						num[v] += num[*it];
					}
				}
			}
		}
	}
}

int main(){
	
	scanf("%d%d%d%d",&n,&m,&st,&ed);
	for(int i=0;i<n;i++){
		scanf("%d",&weight[i]);
	}
	int u,v,wt;
	for(int i=0;i<m;i++){
		scanf("%d%d%d",&u,&v,&wt);
		adj[u].push_back(node(v,wt));
		adj[v].push_back(node(u,wt));
	}
	bellman(st);
	printf("%d %d\n",num[ed],w[ed]);
	return 0;
	

	
	return 0;
}

const int maxv = 510;
const int inf = 1000000000;

int n,d[maxv],num[maxv];
bool inq[maxv];

bool spfa(int s){
	memset(inq,false,sizeof(inq));
	memset(num,0,sizeof(num));
	fill(d,d+maxv,inf);
	
	queue<int> q;
	q.push(s);
	inq[s] = true;
	num[s]++;
	d[s]=0;
	
	while(!q.empty()){
		int u = q.front();
		q.pop();
		inq[u] = false;
		for(int j=0;j<adj[u].size();j++){
			int v = adj[u][j].v;
			int dis=adj[u][j].dis;
			
			if(d[u]+dis<d[v]){
				d[v] = d[u] + dis;
				if(!inq[v]){
					q.push(v);
					inq[v] = true;
					num[v]++;
					if(num[v]>=n) return false;
				}
			}
			
		}
	}
	return true;
}