HDU 3498 whosyourdaddy【Dancing Links重复覆盖】

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

const int maxn = 60*60 + 10;
const int oo = 1 << 30;
const int maxrow = 60;
const int maxcol = 60;
int mtx[maxrow][maxcol];
int n, m, ans;

int totRow, totCol, head, idx;
int L[maxn], R[maxn], U[maxn], D[maxn];
int RH[maxn], CH[maxn], S[maxn];

void initMtx()
{
memset(mtx, 0, sizeof(mtx));
for (int i = 0; i < n; ++i) {
mtx[i][i] = 1;
}
int a, b;
for (int i = 0; i < m; ++i) {
scanf("%d%d", &a, &b);
a--; b--;
mtx[a][b] = mtx[b][a] = 1;
}
}

int newNode(int up, int down, int left, int right)
{
U[idx] = up;    D[idx] = down;
L[idx] = left;  R[idx] = right;
U[down] = D[up] = L[right] = R[left] = idx;
return idx++;
}

void build()
{
idx = maxn - 1;
head = newNode(idx, idx, idx, idx);
idx = 0;
for (int j = 0; j < totCol; ++j) {
newNode(idx, idx, L[head], head);
CH[j] = j;  S[j] = 0;
}
for (int i = 0; i < totRow; ++i) {
int k = -1;
for (int j = 0; j < totCol; ++j) {
if (!mtx[i][j]) continue;
if (-1 == k) {
k = newNode(U[CH[j]], CH[j], idx, idx);
RH[k] = i;  CH[k] = j;  S[j]++;
} else {
k = newNode(U[CH[j]], CH[j], k, R[k]);
RH[k] = i;  CH[k] = j;  S[j]++;
}
}
}
}

void remove(int c)
{
for (int i = D[c]; i != c; i = D[i]) {
L[R[i]] = L[i]; R[L[i]] = R[i]; /*S[CH[i]]--;*/
}
}

void resume(int c)
{
for (int i = U[c]; i != c; i = U[i]) {
L[R[i]] = R[L[i]] = i; /*S[CH[i]]++;*/
}
}

/*估价函数*/
int h()
{
bool vis[maxcol];
memset(vis, false, sizeof(vis));
int ret = 0;
for (int i = R[head]; i != head; i = R[i]) {
if (!vis[i]) {
ret++;
vis[i] = true;
for (int j = D[i]; j != i; j = D[j]) {
for (int k = R[j]; k != j; k = R[k]) {
vis[CH[k]] = true;
}
}
}
}
return ret;
}

void dance(int cnt)
{
if (cnt + h() >= ans) { //此处写成">"会TLE
return ;
}
if (R[head] == head) {
ans = cnt;
return ;
}
int c, Min = oo;
for (int i = R[head]; i != head; i = R[i]) {
if (S[i] < Min) {
Min = S[i]; 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);
}

dance(cnt + 1);

for (int j = L[i]; j != i; j = L[j]) {
resume(j);
}
resume(i);
}
return ;
}

int main()
{
while (scanf("%d%d", &n, &m) != EOF) {
totRow = n; totCol = n;
initMtx();
build();
ans = oo;
dance(0);
printf("%d\n", ans);
}
return 0;
}