hdu1874 Dijkstra(堆优化)+floyd

最新推荐文章于 2022-05-06 18:25:21 发布

原创最新推荐文章于 2022-05-06 18:25:21 发布 · 456 阅读

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#dijkstra #优化 #floyd

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本文通过C++实现了两种图算法：Dijkstra算法和Floyd算法。Dijkstra算法用于寻找单源最短路径，而Floyd算法则可以求解任意两点间的最短路径。文中详细展示了两种算法的实现过程及关键步骤。

//感谢jianshen

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstdlib>
#include <queue>
#include <cstring>
#include <utility>
#define MAXN 2510
#define MAXM 6210

using namespace std;
int n,m,s,t;
typedef pair<int ,int> PII;
struct edge {
	int v, w;
	edge *next;
	void add(int y, int z, edge *&head){ v = y; w = z; next = head; head = this; }
}Te[MAXM*2],*Pe=Te,*head[MAXN*2];

void add_edge(int x, int y, int z) {
	Pe++->add(y, z, head[x]);
}

int dist[MAXN];
bool visit[MAXN];

void dijkstra(int x) {
	priority_queue<PII>q;
	while (!q.empty()) q.pop();
	memset(dist, 0x3f, sizeof(dist));
	memset(visit, 0, sizeof(visit));
	dist[x] = 0;

	q.push(make_pair(0, x));
	while (!q.empty()) {
		while (!q.empty() && visit[q.top().second]) q.pop();
		if (q.empty()) break;
		PII t = q.top(); q.pop();
		int i = t.second;
		dist[i] = -t.first;
		visit[i]=true;
		for (edge *p = head[i]; p; p = p->next)
			if (!visit[p->v]) q.push(make_pair(-(dist[i] + p->w), p->v));
	}
}
void init()
{
     memset(head, 0, sizeof(head));
     Pe=Te;
	for(int i=1;i<=m;i++)
	{
		int x,y,z;
		scanf("%d%d%d",&x,&y,&z);
		add_edge(x,y,z);
        add_edge(y,x,z);
	}
    scanf("%d%d",&s,&t);
}
int main()
{
    while(scanf("%d%d",&n,&m)==2){
        init();
        if(s==t){cout<<0<<endl;continue;}
        dijkstra(s);
        cout<<(dist[t]==0x3f3f3f3f?-1:dist[t])<<endl;
    }
}

floyd

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
using namespace std;
const int MAXN = 555;
int f[MAXN][MAXN], s, t, n, m;
int main()
{
    while (~scanf("%d%d", &n, &m))
    {
        memset(f, 0x3f, sizeof(f));
        int tmp=f[1][1];
        for (int i = 1; i <= m; i++)
        {
            int u, v, w;
            scanf("%d%d%d", &u, &v, &w);
            ++u; ++v;//注意下标位置
            //printf("Add %d %d %d\n", u, v, w);
            f[u][v] = f[v][u] = min(w, f[u][v]);//邻接矩阵,重边= =
        }
        scanf("%d%d", &s, &t);
        if(s == t) {//特判
            cout<<0<<endl;
            continue;
        }
        for (int k = 1; k <= n; k++)
            for (int i = 1; i <= n; i++)
                for (int j = 1; j <= n; j++)
                    if (f[i][j] > f[i][k] + f[k][j])
                        f[i][j] = f[i][k] + f[k][j];
        printf("%d\n", f[s + 1][t + 1]==tmp?-1:f[s+1][t+1]);
    }
    return 0;
}