UV 10318-Security Panel dfs pruning

UV 10318-Security Panel dfs pruning

ACM

Address: Ultraviolet A 10318-Security Panel

Question:
This is similar to the lighting question. When a lamp is selected, the lighting game changes its status and the surrounding lights.
However, we have a special on-and-off technique, which provides a location for changing the status, rather than changing around the clock.
Ask the minimum switch step from shutting down all to turning on all.

Analysis:
Obviously, it is unnecessary to click twice or more times in one location. Therefore, you only need to select or not to select a location and use dfs. However, if there is any possibility of brute force, the complexity is 2 ^ 25, and timeout occurs. Therefore, pruning is required.
Because the impact range is 3*3, the switch cannot affect the status before the two rows. You only need to judge before going to the next row.
Because the data size is small, this pruning is enough.

Code:

/**  Author:      illuz 
 
  *  File:        10318.cpp*  Create Date: 2014-06-29 19:51:39*  Descripton:   */#include 
  
   #include 
   
    #include 
    
     #include using namespace std;const int dx[] = {-1,-1,-1, 0, 0, 0, 1, 1, 1};const int dy[] = {-1, 0, 1,-1, 0, 1,-1, 0, 1};const int N = 6;int r, c, cas;int change[3*3], lit[N][N], prs[N*N], ans[N*N], cnt;char str[4];bool check(int l1) {if (l1 >= 0) {for (int i = 0; i < c; i++) {if (!lit[l1][i]) {return false;}}}return true;}void pressfunc(int x, int y) {for (int i = 0; i < 9; i++) {if (change[i]) {int tx = x + dx[i], ty = y + dy[i];if (tx >= 0 && tx < r && ty >= 0 && ty < c) {lit[tx][ty] = !lit[tx][ty];}}}}void dfs(int x, int y, int press) {if (y == c) {if (x == r - 1) {// check if all lightfor (int i = 0; i < r; i++) {if (!check(i)) {return;}}// if all light, update the ansif (press < cnt) {cnt = press;for (int i = 0; i < press; i++) {ans[i] = prs[i];}}return;} else {if (!check(x - 2)) {// if not all light in line x - 2return;}x++;y = 0;}}// not pressdfs(x, y + 1, press);// presspressfunc(x, y);prs[press] = c * x + y + 1;dfs(x, y + 1, press + 1);pressfunc(x, y);// roll back}int main() {while (~scanf("%d%d", &r, &c) && (r || c)) {// inputfor (int i = 0; i < 3; i++) {scanf("%s", str);for (int j = 0; j < 3; j++) {change[i*3+j] = str[j] == '*' ? 1 : 0;}}// initmemset(lit, 0, sizeof(lit));cnt = r * c + 1;// solveprintf("Case #%d\n", ++cas);dfs(0, 0, 0);if (cnt != r * c + 1) {for (int i = 0; i < cnt - 1; i++) {printf("%d ", ans[i]);}printf("%d\n", ans[cnt - 1]);} else {puts("Impossible.");}}return 0;}