UVa 10305 - Ordering Tasks

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传送门UVa 10305 - Ordering Tasks

拓扑排序的入门题。

刚开始理解起来有一点困难，现在还是半知半解，当初学树的时候也这样。过几天再来看看。

#include <cstdio>#include <cstring>using namespace std;const int MAXN = 105;int graph[MAXN][MAXN];int n, t;int topo[MAXN];int c[MAXN];bool DFS(int u);bool toposort();int main(){    //freopen("input.txt", "r", stdin);    int m, i;    while (scanf("%d%d", &n, &m))    {        int u, v;        if (n + m == 0)            break;        memset(graph, 0, sizeof(graph));        for (i = 0; i < m; i++)        {            scanf("%d%d", &u, &v);            graph[u][v] = 1;        }        if (toposort())        {            for (i = 0; i < n - 1; i++)                printf("%d ", topo[i]);            printf("%d\n", topo[i]);        }    }    return 0;}bool toposort(){    int i;    t = n;    memset(c, 0, sizeof(c));    for (i = 1; i <= n; i++)        if (!c[i] && !DFS(i))            return false;    return true;}bool DFS(int u){    c[u] = -1;    for (int v = 1; v <= n; v++)    {        if (graph[u][v])        {            if (c[v] < 0)                return false;            else if (!c[v] && !DFS(v))                return false;        }    }    c[u] = 1;    topo[--t] = u;    return true;}

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