思路：採用n*logn的優化迪傑斯特拉演算法，求出最短路，反向建圖以後，在dfs搜尋即可，用set+vector記錄路徑，注意vector的傳遞需要加引用（用string 就不用加引用）。

實現非常簡單，直接看程式碼就行。

#include <bits/stdc++.h>
using namespace std;
const int maxn=100;
typedef long long ll;
struct Edge
{
    int u,v,w,next;
}edge[maxn<<1],edge2[maxn<<1];
int head[maxn];
int num;
void addEdge(int u,int v,int w)
{
    edge[num].u=u;
    edge[num].v=v;
    edge[num].w=w;
    edge[num].next=head[u];
    head[u]=num++;
}
int num2,head2[maxn];

void addEdge2(int u,int v,int w)
{
    edge2[num2].u=u;
    edge2[num2].v=v;
    edge2[num2].w=w;
    edge2[num2].next=head2[u];
    head2[u]=num2++;
}

void init()
{
    memset(head,-1,sizeof(head));
	memset(head2,-1,sizeof(head2));
	num2=0;
    num=0;
}
struct node
{
    int num, val; //存編號 和距離
    node(int _num=0, int _val=0):num(_num), val(_val) {}
    bool operator <(const node &tmp) const
    {
        return val > tmp.val;
    }
    node()=default;
};
int n,s,t;
bool vis[maxn];
int dis[maxn];
int path[maxn];
void dijkstra(int st) //起點
{
    priority_queue<node> que;
    memset(dis, 0x3f, sizeof(dis));
    memset(vis, 0, sizeof(vis));
    dis[st] = 0;
    que.push(node(st, 0));
    while(!que.empty())
    {
        node p = que.top();
        que.pop();
        int nown = p.num;
        if(vis[nown])
            continue;
        vis[nown] = true;
        for(int i=head[nown]; i!=-1; i=edge[i].next)
        {
            Edge e = edge[i];
            if(dis[e.v] > dis[nown] + e.w && !vis[e.v])
            {
                dis[e.v] = dis[nown] + e.w;
                que.push(node(e.v,dis[e.v]));
            }
        }
    }
}
set<vector<int>> se;
void prinPath(int s,vector<int> &vec)
{
	vec.push_back(s);
	if(s==::s) 
	{
		reverse(vec.begin(),vec.end());
		se.insert(vec);
		vec.clear();
		vec.push_back(::t);
		return;
	}
	for(int i=head2[s];i!=-1;i=edge2[i].next)
	{
		int v=edge2[i].v,w=edge2[i].w;
		if(dis[v]==dis[s]-w)
		{
			//printf("%d...%d\n",v,s);
			prinPath(v,vec);
			//return;
		}
	}
	// reverse(vec.begin(),vec.end());
	// se.insert(vec);
}
int main()
{
    #ifndef ONLINE_JUDGE
        freopen("in.txt","r",stdin);
        freopen("out.txt","w",stdout);
    #endif
    int Case=0;
    while(scanf("%d",&n)!=EOF)
    {
		se.clear();
		init();
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=n;j++)
            {
                int w;
                scanf("%d",&w);
                if(w==-1) continue;
                addEdge(i,j,w);
				addEdge2(j,i,w);
            }
        }
        scanf("%d%d",&s,&t);
        dijkstra(s);
        printf("Case %d\n",++Case);
        printf("The least distance from %d -> %d is %d\n",s,t,dis[t]);
		vector<int> vec;
		prinPath(t,vec);
		set<vector<int> >::iterator it;
		printf("最短路徑有:%d 條\n",se.size());
		printf("the path is ");
		for(it=se.begin();it!=se.end();it++){
		vector<int> ans=*it;
		for(int i=0;i<ans.size()-1;i++)
		{
			printf("%d->",ans[i]);
		}
		printf("%d\n",ans[ans.size()-1]);
		cout<<endl;
		}
    }
    return 0;
}