hdu 4687 Boke and Tsukkomi

Dancing link twice.

Find the maximum combination numbers in the first time.

Enumerate each node, dancing.

If the new result is not optimaze, then push it into ans.

#include <cstdio>
#include <vector>
#include <bitset>
#include <cstdlib>
#include <cstring>
#include <iostream>
using namespace std;
const int M = 200;

// exact
struct dancing {
#define dfor(c, a, b) for (int c = a[b]; c != b; c = a[c])
  static const int row_size = 220, column_size = 220,
               total_size = row_size*column_size;
  typedef int row[row_size],
          column[column_size],
          total[total_size];
  total l, r, u, d, in_column, in_row;
  bitset<50> use;
  column s;
  int index, current_row, row_head, limit, mx, rn;
  void init(int n, int m) {
    rn = m;
    limit = 0;
    index = ++n;
    for (int i = 0; i < n; i++) {
      l[i] = (i - 1 + n) % n;
      r[i] = (i + 1) % n;
      u[i] = d[i] = i;
    }
    current_row = 0;
    memset(s, 0, sizeof(s));
    use = ans = bitset<50>();
    mx = -1;
  }
  void push(int i, int j) {
    i++; j++;
    if (current_row < i) {
      row_head = l[index] = r[index] = index;
      current_row = i;
    }
    l[index] = l[row_head]; r[index] = row_head;
    r[l[row_head]] = index; l[row_head] = index;
    u[index] = u[j]; d[index] = j;
    d[u[j]] = index; u[j] = index;
    s[j]++;
    in_row[index] = i;
    in_column[index++] = j;
  }
  void exactly_remove(int c) {
    l[r[c]] = l[c];
    r[l[c]] = r[c];
    dfor(i, d, c) {
      dfor (j, r, i) {
        u[d[j]] = u[j];
        d[u[j]] = d[j];
        s[in_column[j]]--;
      }
    }
  }
  void exactly_resume(int c) {
    dfor(i, u, c) {
      dfor(j, l, i) {
        s[in_column[j]]++;
        d[u[j]] = u[d[j]] = j;
      }
    }
    r[l[c]] = l[r[c]] = c;
  }
  bool exactly_dance(int step = 0) {
    limit = max(limit, step);
    if (limit == mx) return 1;
    if (!r[0]) return 0;
    int has = rn-use.count();
    if (!has || step+has < limit || step+has < mx) return 0;
    int x = r[0];
    dfor(i, r, 0) {
      if (s[i] && s[i] < s[x] || !s[x]) {
        x = i;
      }
    }
    exactly_remove(x);
    dfor(i, d, x) {
      use[in_column[i]] = 1;
      dfor(j, r, i) {
        exactly_remove(in_column[j]);
      }
      if (exactly_dance(step + 1)) {
        return 1;
      }
      dfor(j, l, i) {
        exactly_resume(in_column[j]);
      }
      use[in_column[i]] = 0;
    }
    exactly_resume(x);
    return 0;
  }
#undef dfor
};
dancing dlx;

struct com {
  int b, t;
  void input() {
    scanf("%d%d", &b, &t);
  }
} c[M];
int n, m, g[M][50];

int main() {
  for ( ; ~scanf("%d%d", &n, &m); ) {
    memset(g, 0, sizeof(g));
    dlx.init(n, m);
    for (int i = 0; i < m; i++) {
      c[i].input();
      if (c[i].b > c[i].t) swap(c[i].b, c[i].t);
      int b = c[i].b, t = c[i].t;
      g[i][b] = g[i][t] = 1;
      dlx.push(i, b-1);
      dlx.push(i, t-1);
    }
    dlx.exactly_dance();
    int limit = dlx.limit;
    vector<int> ans;
    int ban[M] = {0};
    for (int i = 0; i < m; i++) {
      int tm = m;
      memset(ban, 0, sizeof(int)*m);
      for (int j = 0; j < m; j++) if (i != j)
        if (g[j][c[i].b] || g[j][c[i].t]) {
          ban[j] = 1;
          tm--;
        }
      dlx.init(n, tm);
      for (int j = 0; j < m; j++) if (!ban[j]) {
        dlx.push(j, c[j].b-1);
        dlx.push(j, c[j].t-1);
      }
      dlx.mx = limit;
      dlx.exactly_dance();
      if (limit != dlx.limit) ans.push_back(i+1);
    }
    printf("%d\n", (int)ans.size());
    if (!ans.size()) puts("");
    else for (int i = 0; i < ans.size(); i++)
      printf("%d%c", ans[i], i < ans.size()-1? ' ': '\n');
  }
  return 0;
}