洛谷 P2921 [USACO08DEC]在农场万圣节Trick or Treat on the Farm

今后需要改良一下拓扑排序,不要一遍一遍扫。只要抓到一个入度为0的就紧追不舍即可,一遍一遍的扫很耗费时间的。。。具体可看代码。

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#include<iostream>
#include<algorithm>
#define ll long long
#define pii pair<int,int>
#define PINF 0x7fffffff
#define NINF 0x80000000
using namespace std;
int n;
int nxt[100005];
bool visited[100005];
int allocated[100005];
int alloc_ptr = 0;
int allocate_dis[100005];
int chainDis[100005];
int inDegree[100005];
inline void removeInDegree(int node) {
    if (inDegree[node] != 0)return;
    inDegree[node]--;
    inDegree[nxt[node]]--;
    removeInDegree(nxt[node]);
}
inline int dfsRing(int alloc, int node) {
    if (visited[node])return 0;
    visited[node] = true;
    allocated[node] = alloc;
    return 1 + dfsRing(alloc, nxt[node]);
}
inline int dfsToRing(int node) {
    if (chainDis[node] != 0)return chainDis[node];
    if (allocated[node])return chainDis[node] = allocate_dis[allocated[node]];
    else return chainDis[node] = 1 + dfsToRing(nxt[node]);
}
int main() {
    ios::sync_with_stdio(false);
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> nxt[i];
        inDegree[nxt[i]]++;
    }
    for (int i = 1; i <= n; i++) {
        if (inDegree[i] == 0)removeInDegree(i);
    }
    for (int i = 1; i <= n; i++) {
        if (inDegree[i] <= 0 || allocated[i]) continue;
        alloc_ptr++;
        allocate_dis[alloc_ptr] = dfsRing(alloc_ptr, i);
    }
    for (int i = 1; i <= n; i++) {
        if (allocated[i])cout << allocate_dis[allocated[i]] << endl;
        else cout << dfsToRing(i) << endl;
    }
}

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