CSP2019 D1T3 树上的数 （贪心+并查集）

题解

因为博主退役了，所以题解咕掉了。先放个代码

CODE

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 2005;
int n, ps[MAXN], ans[MAXN], fir[MAXN], to[MAXN<<1], nxt[MAXN<<1], cntE, Mn;
int f[MAXN][MAXN<<1], cnt[MAXN]; bool bf[MAXN<<1], st[MAXN], ed[MAXN];
inline void link(int u, int v) {
	to[++cntE] = v; nxt[cntE] = fir[u]; fir[u] = cntE;
	to[++cntE] = u; nxt[cntE] = fir[v]; fir[v] = cntE;
}
int find(int u, int x) { return !f[u][x] ? x : f[u][x] = find(u, f[u][x]); }
void dfs(int u, int ff) {
	if(ff && !f[u][ff] && !ed[u] && (find(u, 2*n+2) != ff || cnt[u] == 1)) Mn = min(Mn, u);
	for(int i = fir[u]; i; i = nxt[i]) if(i^ff)
		if( (!ff && !st[u] && !bf[i] && (find(u, i) != 2*n+3 || cnt[u] == 1))
		|| (ff && !f[u][ff] && !bf[i] && find(u, i) != ff && (find(u, 2*n+2) != ff || find(u, i) != 2*n+3 || cnt[u] == 2)))
			dfs(to[i], i^1);
}
bool mdf(int u, int ff) {
	if(u == Mn) { f[u][ff] = 2*n+3, ed[u] = 1; return 1; }
	for(int i = fir[u]; i; i = nxt[i]) if((i^ff) && mdf(to[i], i^1)) {
		if(!ff) f[u][2*n+2] = i, st[u] = 1, bf[i] = 1;
		else f[u][ff] = i, --cnt[u], bf[i] = 1;
		return 1;
	}
	return 0;
}
int main(){
	freopen("tree.in","r",stdin);
	freopen("tree.out","w",stdout);
	int T; scanf("%d", &T);
	while(T--) {
		memset(f, 0, sizeof f);
		memset(bf, 0, sizeof bf);
		memset(st, 0, sizeof st);
		memset(ed, 0, sizeof ed);
		memset(fir, 0, sizeof fir);
		memset(cnt, 0, sizeof cnt);
		cntE = 1;
		scanf("%d",&n);
		for(int i = 1; i <= n; ++i)	scanf("%d", &ps[i]);
		for(int i = 1, x, y; i < n; ++i) scanf("%d%d", &x, &y), ++cnt[x], ++cnt[y], link(x, y);
		for(int i = 1; i <= n; ++i) Mn = n, dfs(ps[i], 0), mdf(ps[i], 0), ans[i] = Mn;
		for(int i = 1; i <= n; ++i) printf("%d%c", ans[i], " \n"[i==n]);
	}
}