HDU 3498 whosyourdaddy【Dancing Links重复覆盖】

有n个单位的敌人，对某个敌人进行攻击时该敌人以及与其直接相邻的敌人都会被消灭。问消灭所有敌人所需的最少攻击次数。

重复覆盖问题。我把此题贴出来是想说剪枝优化很有必要，一个小细节就能决定是TLE还是AC。

#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;}