BZOJ4010 [HNOI2015]菜肴制作

  1 /**************************************************************
  2     Problem: 4010
  3     User: rausen
  4     Language: C++
  5     Result: Accepted
  6     Time:900 ms
  7     Memory:3936 kb
  8 ****************************************************************/
  9  
 10 #include <cstdio>
 11 #include <cstring>
 12 #include <queue>
 13  
 14 using namespace std;
 15 const int N = 1e5 + 5;
 16  
 17 struct edge {
 18     int next, to;
 19     edge(int _n = 0, int _t = 0) : next(_n), to(_t) {}
 20 } e[N];
 21  
 22 int n, m;
 23 int first[N], tot;
 24 int deg[N], q[N];
 25 int t[N], NOW, v[N];
 26 int ans[N];
 27 priority_queue <int> h;
 28  
 29 inline int read();
 30  
 31 inline void add_edge(int x, int y) {
 32     e[++tot] = edge(first[x], y), first[x] = tot;
 33     ++deg[y];
 34 }
 35  
 36 #define p q[l]
 37 #define y e[x].to
 38 bool check_circle() {
 39     static int i, l, r, x;
 40     for (r = 0, i = 1; i <= n; ++i) if (deg[i] == 0) q[++r] = i;
 41     for (l = 1; l <= r; ++l)
 42         for (x = first[p]; x; x = e[x].next)
 43             if (--deg[y] == 0) q[++r] = y;
 44     return r != n;
 45 }
 46  
 47 inline int bfs(int s) {
 48     static int l, r, x;
 49     ++NOW;
 50     q[l = r = 1] = s;
 51     for (; l <= r; ++l)
 52         for (x = first[p]; x; x = e[x].next) if (!v[y]) {
 53             ++deg[y];
 54             if (t[y] != NOW)
 55                 q[++r] = y, t[y] = NOW;
 56         }
 57 }
 58 #undef p
 59  
 60 inline void get(int s) {
 61     static int p, x;
 62     while (!h.empty()) h.pop();
 63     h.push(s), v[s] = 1;
 64     while (!h.empty()) {
 65         p = h.top(), h.pop();
 66         ans[++ans[0]] = p;
 67         for (x = first[p]; x; x = e[x].next) if (!v[y])
 68             if (--deg[y] == 0) h.push(y), v[y] = 1;
 69     }
 70 }
 71 #undef y
 72  
 73 int main() {
 74     int T, i, x, y;
 75     T = read();
 76     while (T--) {
 77         n = read(), m = read(), tot = NOW = 0;
 78         memset(first, 0, sizeof(first));
 79         memset(v, 0, sizeof(v));
 80         memset(deg, 0, sizeof(deg));
 81         memset(t, 0, sizeof(t));
 82         for (i = 1; i <= m; ++i) {
 83             x = read(), y = read();
 84             add_edge(y, x);
 85         }
 86         if (check_circle()) {
 87             puts("Impossible!");
 88             continue;
 89         }
 90         for (i = 1; i <= n; ++i) if (!v[i]) {
 91             bfs(i);
 92             get(i);
 93             for (; ans[0]; --ans[0]) printf("%d ", ans[ans[0]]);
 94         }
 95         puts("");
 96     }
 97     return 0;
 98 }
 99  
100 inline int read() {
101     static int x;
102     static char ch;
103     x = 0, ch = getchar();
104     while (ch < ‘0‘ || ‘9‘ < ch)
105         ch = getchar();
106     while (‘0‘ <= ch && ch <= ‘9‘) {
107         x = x * 10 + ch - ‘0‘;
108         ch = getchar();
109     }
110     return x;
111 }