HDU 5046 Airport

题目链接

题意：给定一些机场。要求选出K个机场，使得其它机场到其它机场的最大值最小

思路：二分+DLX反复覆盖去推断就可以

代码：

#include <cstdio>#include <cstring>using namespace std;const int MAXNODE = 4005;const int MAXM = 65;const int MAXN = 65;const int INF = 0x3f3f3f3f;int K;struct DLX {	int n, m, size;	int U[MAXNODE], D[MAXNODE], R[MAXNODE], L[MAXNODE], row[MAXNODE], col[MAXNODE];	int H[MAXN], S[MAXM];	int ansd, ans[MAXN];	void init(int n, int m) {		this->n = n;		this->m = m;		ansd = INF;		for(int i = 0; i <= m; i++) {			S[i] = 0;			U[i] = D[i] = i;			L[i] = i - 1;			R[i] = i + 1;		}		R[m] = 0; L[0] = m; 		size = m;		for(int i = 1; i <= n; i++)			H[i] = -1;	}	void Link(int r, int c) {		++S[col[++size] = c];		row[size] = r;		D[size] = D[c];		U[D[c]] = size;		U[size] = c;		D[c] = size;		if(H[r] < 0) H[r] = L[size] = R[size] = size;		else {			R[size] = R[H[r]];			L[R[H[r]]] = size;			L[size] = H[r];			R[H[r]] = size;		}	}	void remove(int c) {		for(int i = D[c]; i != c; i = D[i]) {			L[R[i]] = L[i];			R[L[i]] = R[i];		}	}	void resume(int c) {		for(int i = U[c]; i != c; i = U[i])			L[R[i]] = R[L[i]] = i;	}	bool v[MAXNODE];	int f() {		int ret = 0;		for(int c = R[0]; c != 0; c = R[c]) v[c] = true;		for(int c = R[0]; c != 0; c = R[c]) {			if(v[c]) {				ret++;				v[c] = false;				for(int i = D[c]; i != c; i = D[i])					for(int j = R[i]; j != i; j = R[j])						v[col[j]] = false;			}		}		return ret;	}	bool Dance(int d) {		if(d + f() > K) return false;		if(R[0] == 0) {			return d <= K;		}		int c = R[0];		for(int i = R[0]; i != 0; i = R[i]) {			if(S[i] < S[c])				c = i;		}		for(int i = D[c]; i != c; i = D[i]) {			remove(i);			for(int j = R[i]; j != i; j = R[j]) remove(j);			ans[d] = row[i];			if (Dance(d + 1)) return true;			for(int j = L[i]; j != i; j = L[j]) resume(j);			resume(i);		}		return false;	}} gao;typedef long long ll;int T, n;const int N = 65;struct City {	ll x, y;	void read() {		scanf("%I64d%I64d", &x, &y);	}} c[N];ll dis(City a, City b) {	ll dx = a.x - b.x; if (dx < 0) dx = -dx;	ll dy = a.y - b.y; if (dy < 0) dy = -dy;	return dx + dy;}int main() {	int cas = 0;	scanf("%d", &T);	while (T--) {		scanf("%d%d", &n, &K);		for (int i = 1; i <= n; i++) c[i].read();		ll l = 0, r = 100000000000LL;		while (l < r) {			ll mid = (l + r) / 2;			gao.init(n, n);			for (int i = 1; i <= n; i++) {				for (int j = 1; j <= n; j++) {					if (dis(c[i], c[j]) <= mid)						gao.Link(i, j);				}			}			if (gao.Dance(0)) r = mid;			else l = mid + 1;		}		printf("Case #%d: %I64d\n", ++cas, l);	}	return 0;}