CF963B Destruction of a Tree

思路：

根据节点度数的奇偶性确定删除节点的先后顺序，然后进行拓扑排序。

实现：

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 200005;
vector<int> G[MAXN], G2[MAXN];
int in[MAXN], n;
int build(int u, int p)
{
    if (!G[u].size()) { G2[p].push_back(u); in[u]++; return 1; }
    int cnt = 0;
    for (int i = 0; i < G[u].size(); i++) cnt += build(G[u][i], u);
    if (cnt & 1) { G2[u].push_back(p); in[p]++; return 0; }
    else { G2[p].push_back(u); in[u]++; return 1; }
}
void toposort()
{
    queue<int> q;
    for (int i = 1; i <= n; i++) if (!in[i]) q.push(i);
    while (!q.empty())
    {
        int x = q.front(); q.pop();
        cout << x << endl;
        for (auto it: G2[x])
        {
            in[it]--;
            if (!in[it]) q.push(it);
        }
    }
}
int main()
{
    int x, root;
    while (cin >> n)
    {
        for (int i = 1; i <= n; i++)
        {
            G[i].clear(); G2[i].clear();
        }
        memset(in, 0, sizeof in);
        for (int i = 1; i <= n; i++)
        {
            cin >> x;
            if (x) G[x].push_back(i);
            else root = i;
        }
        int ans = build(root, 0);
        if (G2[0].size()) in[root]--;
        if (ans & 1)
        {
            cout << "YES" << endl;
            toposort();
        }
        else cout << "NO" << endl;
    }
    return 0;
}