题目描述
Link
Solution
题目要求中说尽可能让编号小的优先，还要满足做菜顺序，于是我们可以将队列换成优先队列，然后再反向建图跑拓扑就行了，最后倒序输出。
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| #include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#define MAXN 100101
struct Edge {
int v, nx;
}e[MAXN << 1];
int head[MAXN], ecnt, n, T, m, x, y, ent[MAXN], st[MAXN], top, fl;
void add(int f, int t) {
e[++ecnt] = (Edge) {t, head[f]};
head[f] = ecnt;
}
int main() {
scanf("%d", &T);
while (T--) {
memset(head, 0, sizeof(head));
memset(ent, 0, sizeof(ecnt));
memset(ent, 0, sizeof(ent));
ecnt = 0;
top = 0;
scanf("%d%d", &n, &m);
for (int i = 1; i <= m; i++) {
scanf("%d%d", &x, &y);
add(y, x);
ent[x]++;
}
std::priority_queue <int> q;
for (int i = 1; i <= n; i++) {
if (!ent[i]) q.push(i);
}
while (!q.empty()) {
int u = q.top();
st[++top] = u;
q.pop();
for (int i = head[u]; i; i = e[i].nx) {
int to = e[i].v;
ent[to]--;
if (!ent[to]) q.push(to);
}
}
fl = 0;
for (int i = 1; i <= n; i++) {
if (ent[i] >= 1) fl = 1;
}
if (fl) {
puts("Impossible!");
continue;
}
for (int i = top; i >= 1; i--) {
printf("%d ", st[i]);
}
puts("");
}
}
|
