UVA193

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题意：使相连的两点都不能为黑色，求所染的色中黑色的数目最大

思路：先将所有点都染为白色，然后再进行染黑色，如果染黑色，则进行下一次递归时，要记得数目num+1，如果没有的话，就不要+1；

#include<stdio.h>#include<string.h>#define N 105int color[N], black[N];int map[N][N];int Max, n, a, b, num;int  dfs(int x, int cnt){int flag = 1;if (cnt > Max){Max = cnt;for(int i = 1; i <= n; i++)black[i] = color[i];}if (cnt + n - x + 1 <= Max)return 0;for(int i = 1; i <= n; i++)if (map[x][i] == 1 && color[i] == 1){flag = 0;break;}if (flag){color[x] = 1;dfs(x + 1, cnt + 1);color[x] = 0;}dfs(x + 1, cnt);return 0;}int main(){int cas, m;scanf("%d", &cas);while (cas--){scanf("%d%d", &n, &m);memset(map, 0, sizeof(map));memset(color, 0, sizeof(color));memset(black, 0, sizeof(black));for(int i = 0; i < m; i++){scanf("%d%d", &a, &b);map[a][b] = 1;map[b][a] = 1;}Max = 0, num = 0;dfs(1, 0);printf("%d\n", Max);for(int i = 1; i <= n; i++){if (black[i]){++num;  printf("%d",i);  if (num == Max) printf("\n"); else printf(" ");  }}}return 0;}