hdu1285 拓扑排序

最新推荐文章于 2019-02-22 10:08:26 发布

原创最新推荐文章于 2019-02-22 10:08:26 发布 · 525 阅读

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本文详细介绍了拓扑排序的应用，并通过邻接矩阵和邻接链表两种方式实现了序列的排序过程。同时利用优先队列优化了排序效率。

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简单的拓扑排序应用

采用邻接矩阵：

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
#define maxn 505
int map[maxn][maxn];
int indegree[maxn], n, m;
int main()
{
    while (cin >> n >> m)
    {
        memset(map, 0, sizeof(map));
        memset(indegree, 0, sizeof(indegree));
        while (m--)
        {
            int a, b;
            cin >> a >> b;
            if (!map[a][b])
            {
                map[a][b] = 1;
                ++ indegree[b];
            }
        }
        for (int i=1; i<=n; ++i)
        {
            for (int j=1; j<=n; ++j)
            {
                if (indegree[j]==0)
                {
                    indegree[j] = -1;
                    if (i==1)
                        cout << j;
                    else
                        cout << " " << j;
                    for (int k=1; k<=n; ++k)
                        if (map[j][k])
                        {
                            map[j][k] = 0;
                            -- indegree[k];
                        }
                    break;
                }
            }
        }
        cout << endl;
    }
    return 0;
}

采用邻接链表，使用优先队列是序列有一定的顺序。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>
using namespace std;
#define maxn 10000
struct node
{
    int begin, end;
}edge[maxn];
int head[maxn], indegree[maxn];
/**
1.  3->5
2.  3->6
3.  3->7
edge[1].to = 5;
edge[1].begin = head[3] = -1;
head[3] = 1;
edge[2].to = 6;
edge[2].begin = head[3] = 1;
head[3] = 2;
edge[3].to = 7;
edge[3].begin = head[3] = 2;
head[3] = 3;
*/
int ans[maxn], cnt, n, m;
class cmp
{
    public :
    bool operator()(int x, int y)
    {
        return x>y;
    }
};
int main()
{
    while (cin >> n >> m)
    {
        memset(head, -1, sizeof(head));
        memset(indegree, 0, sizeof(indegree));
        for (int i=1; i<=m; ++i)
        {
            int a, b;
            cin >> a >> b;
            edge[i].end = b;
            edge[i].begin = head[a];
            head[a] = i;
            indegree[b] ++;
        }
        priority_queue<int, vector<int>, cmp> pq;
        for (int i=1; i<=n; ++i)
        {
            if (!indegree[i])
                pq.push(i);
        }
        cnt = 0;
        while (!pq.empty())
        {
            int temp = pq.top();
            pq.pop();
            ans[cnt++] = temp;
            for (int i=head[temp]; i!=-1; i=edge[i].begin)
            {
                indegree[edge[i].end] --;
                if (!indegree[edge[i].end])
                    pq.push(edge[i].end);
            }
        }
        for (int i=0; i<cnt; ++i)
            i==0 ? cout<<ans[i] : cout<<" "<<ans[i];
        printf("\n");
    }
    return 0;
}