[luoguP1272] 重建道路

Posted 2020-10-01 蒟蒻zht的博客

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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;
}