大家好，又见面了，我是全栈君。
HDU 5046 Airport
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;}
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