Police Stations CodeForces - 796D (bfs)

大意: 给定树, 有k个黑点, 初始满足条件:所有点到最近黑点距离不超过d, 求最多删除多少条边后, 使得原图仍满足条件.

所有黑点开始bfs, 贪心删边.

#include <iostream>

#include <algorithm>

#include <math.h>

#include <cstdio>

#include <set>

#include <map>

#include <string>

#include <vector>

#include <string.h>

#include <queue>

#define PER(i,a,n) for(int i=n;i>=a;--i)

#define REP(i,a,n) for(int i=a;i<=n;++i)

#define hr cout<<'\n'

#define pb push_back

#define mid ((l+r)>>1)

#define lc (o<<1)

#define rc (lc|1)

#define ls lc,l,mid

#define rs rc,mid+1,r

#define x first

#define y second

#define io std::ios::sync_with_stdio(false);

#define endl '\n'

using namespace std;

typedef long long ll;

typedef pair<int,int> pii;

const int P = 1e9+7;

ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}

ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;}

void exgcd(ll a,ll b,ll &d,ll &x,ll &y){b?exgcd(b,a%b,d,y,x),y-=a/b*x:x=1,y=0,d=a;}

ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;}

//head

const int N = 4e5+10, INF = 0x3f3f3f3f;

int n, k, d, t;

int vis[N], vis2[N];

vector<pii> g[N];

int main() {

	scanf("%d%d%d", &n, &k, &d);

	REP(i,1,k) scanf("%d", &t), vis[t]=1;

	REP(i,1,n-1) {

		int u, v;

		scanf("%d%d", &u, &v);

		g[u].pb({v,i}),g[v].pb({u,i});

	}

	queue<int> q;

	vector<int> ans;

	REP(i,1,n) if (vis[i]) q.push(i);

	while (!q.empty()) {

		int u = q.front();q.pop();

		for (auto e:g[u]) {

			if (vis2[e.y]) continue;

			if (vis[e.x]) ans.pb(e.y);

			else q.push(e.x);

			vis[e.x] = vis2[e.y] = 1;

		}

	}

	printf("%d\n",int(ans.size()));

	for (int t:ans) printf("%d ",t);hr;

}