UVA 818 (dfs+ graph + state compression)

Test instructions: There are n rings, numbered from 1 to N, gives a number of interlocking situations, such as a and b for A and b two ring buckle together, each ring can be opened, ask at least how many rings open, and then buckle well, you can make all the ring into a chain.

Puzzle: State compression to all the open loop case enumeration out, and then take to determine whether to set up, update the image after opening the ring G[i][j], and the degree of each point, does not have three cases, 1. Calculates the number of degrees without opening the ring, if greater than 2 indicates that there will be no chain, 2. Take the ring without opening it. Visited on vis[i]++, if vis[i]>=2 illustrates the existence of the ring, 3. If the number of open rings num + 1 is less than the number of chains, the description cannot be linked to a chain. Find the minimum value output.

#include <stdio.h> #include <string.h> #include <algorithm>using namespace std;const int N = 20;int vis[ N], N, Deg[n], g[n][n];void dfs (int u, int fa) {for (int i = 0; i < n; i++) {if (G[u][i] && i! = FA) {vis[i]++; if (Vis[i] < 2) DFS (i, u);}}}  BOOL Solve (int s, int num) {memset (deg, 0, sizeof (deg)), memset (Vis, 0, sizeof (VIS)), int link = 0;for (int i = 0; i < n; i++) {if (S & (1 << i)) {for (int j = 0; J < N; j + +) {if (G[i][j]) g[i][j] = G[j][i] = 0;}} for (int i = 0; i < n; i++) {if (!) ( S & (1 << i)) {for (int j = 0; J < N; j + +) if (G[i][j]) deg[i]++;if (Deg[i] > 2) return false;} for (int i = 0; i < n; i++) {if (!) ( S & (1 << i) &&!vis[i]) {link++;vis[i]++;d fs (i,-1);}} for (int i = 0; i < n; i++) if (Vis[i] >= 2) return false;if (link > num + 1) return False;return true; int main () {int f[n][n], cas = 1, A, B;while (scanf ("%d", &n) = = 1 && N) {memset (f, 0, sizeof (f)); while (scanf ("%d%d", &a, &b) && A! =-1) {f[a-1][b-1] = 1;f[b-1][a-1] = 1;} int res = 0x3f3f, tt = 1 << n;for (int i = 0; i < TT; i++) {for (int j = 0; J < N; j + +) for (int k = 0; K < N k++) g[j][k] = F[j][k];int temp = 0;for (int j = 0; J < N; j + +) if (I & (1 << j)) Temp++;if (Solve (i, temp)) res = min (res, temp);} printf ("Set%d:minimum links to Open is%d\n", cas++, res);} return 0;}

UVA 818 (dfs+ graph + state compression)