[luoguP1272] 重建道路
奇奇怪怪的分组背包。
#include <cstdio> #include <cstring> #include <iostream> #define N 151 #define min(x, y) ((x) < (y) ? (x) : (y)) int n, p, cnt, ans = ~(1 << 31); int head[N], to[N], next[N], f[N][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 dfs(int u) { int i, j, k, v; for(i = head[u]; i ^ -1; i = next[i]) { v = to[i]; dfs(v); for(j = p; j >= 1; j--) for(k = 1; k < j; k++) f[u][j] = min(f[u][j], f[u][j - k] + f[v][k] - 2); } } inline void add(int x, int y) { to[cnt] = y; next[cnt] = head[x]; head[x] = cnt++; } int main() { int i, x, y; n = read(); p = read(); memset(f, 127 / 3, sizeof(f)); memset(head, -1, sizeof(head)); for(i = 1; i <= n; i++) f[i][0] = f[i][1] = 0; for(i = 1; i < n; i++) { x = read(); y = read(); add(x, y); f[x][1]++; f[y][1]++; } dfs(1); for(i = 1; i <= n; i++) ans = min(ans, f[i][p]); printf("%d\n", ans); return 0; }