n <= 300
结果裸的dfs就直接过了。。
枚举每一层,枚举删除每一层的边,然后把删除的边所连接的子树全部删去
代码
#include <vector> #include <cstdio> #include <cstring> #include <iostream> #define N 301 #define min(x, y) ((x) < (y) ? (x) : (y)) #define max(x, y) ((x) > (y) ? (x) : (y)) int n, m, cnt, maxd, ans = ~(1 << 31); int head[N], to[N << 1], next[N << 1], f[N], deep[N], size[N]; std::vector <int> vec[N]; bool vis[N]; inline int read() { int x = 0, f = 1; char ch = getchar(); for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1; for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘; return x * f; } inline void add(int x, int y) { to[cnt] = y; next[cnt] = head[x]; head[x] = cnt++; } inline void dfs(int u) { int i, v; size[u] = 1; maxd = max(maxd, deep[u] = deep[f[u]] + 1); vec[deep[u]].push_back(u); for(i = head[u]; i ^ -1; i = next[i]) { v = to[i]; if(v ^ f[u]) { f[v] = u; dfs(v); size[u] += size[v]; } } } inline void dfs2(int u, int x) { int i, v; vis[u] = x; for(i = head[u]; i ^ -1; i = next[i]) { v = to[i]; if(v ^ f[u]) dfs2(v, x); } } inline void dfs1(int k, int sum) { ans = min(ans, n - sum); if(k == maxd + 1) return; int i, x; for(i = 0; i < vec[k].size(); i++) { x = vec[k][i]; if(!vis[x]) { dfs2(x, 1); dfs1(k + 1, sum + size[x]); dfs2(x, 0); } } } int main() { int i, x, y; n = read(); m = read(); memset(head, -1, sizeof(head)); for(i = 1; i <= m; i++) { x = read(); y = read(); add(x, y); add(y, x); } dfs(1); dfs1(2, 0); printf("%d\n", ans); return 0; }
时间: 2024-10-29 19:07:05