CodeVS 1218NOIP 2012疫情控制

Posted 2020-08-08 abclzr

http://codevs.cn/problem/1218/

比较显然的倍增，但是对于跨过根需要很多讨论，总体思路是贪心。

写了一上午，不想再说什么了

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
typedef long long ll;
const int N = 100003;
int in() {
	int k = 0, fh = 1; char c = getchar();
	for(; c < ‘0‘ || c > ‘9‘; c = getchar())
		if (c == ‘-‘) fh = -1;
	for(; c >= ‘0‘ && c <= ‘9‘; c = getchar())
		k = (k << 3) + (k << 1) + c - ‘0‘;
	return k * fh;
}

struct node {int nxt, to, w;} E[N << 1];
struct data {
	ll left; int from;
	bool operator < (const data &A) const {
		return left < A.left;
	}
} A[N], B[N];
struct data2 {
	int id, dis;
	bool operator < (const data2 &A) const {
		return dis < A.dis;
	}
} P[N];
int f[N][18], n, m, cnt = 0, point[N], L[N], R[N], w[N], Army[N], a[N], nxt[N], upto[N];
ll c[N][18];
bool mark[N];

void ins(int u, int v, int w) {E[++cnt] = (node) {point[u], v, w}; point[u] = cnt;}

void dfs(int x) {
	L[x] = ++cnt;
	w[cnt] = x;
	for(int i = point[x]; i; i = E[i].nxt)	
		if (E[i].to != f[x][0]) {
			f[E[i].to][0] = x;
			c[E[i].to][0] = E[i].w;
			dfs(E[i].to);
		}
	R[x] = cnt;
}

void pushup_mark(int x) {
	if (mark[x]) return;
	bool flag = false, marknow = true;
	for(int i = point[x]; i; i = E[i].nxt)
		if (E[i].to != f[x][0]) {
			pushup_mark(E[i].to);
			flag = true;
			marknow &= mark[E[i].to];
		}
	if (flag) mark[x] = marknow;
}

bool can(ll up) {
	int tmp, tot = 0, tot2 = 0, tot3 = 0; ll ret;
	memset(mark, 0, sizeof(bool) * (n + 1));
	for(int i = 1; i <= m; ++i) {
		ret = up; tmp = Army[i];
		for(int j = 17; j >= 0; --j)
			if (f[tmp][j] && f[tmp][j] != 1 && c[tmp][j] <= ret) {
				ret -= c[tmp][j];
				tmp = f[tmp][j];
			}
		if (c[tmp][0] <= ret) A[++tot] = (data) {ret - c[tmp][0], tmp};
		else mark[tmp] = true;
	}
	
	
	for(int i = point[1]; i; i = E[i].nxt)
		pushup_mark(E[i].to);
	
	for(int i = 1; i <= tot; ++i)
		if (!mark[A[i].from])
			if (A[i].left <= c[A[i].from][0])
				mark[A[i].from] = true;
			else
				B[++tot3] = A[i];
		else
			B[++tot3] = A[i];
	
	for(int i = point[1]; i; i = E[i].nxt)
		if (!mark[E[i].to])
			P[++tot2] = (data2) {E[i].to, c[E[i].to][0]};
	
	stable_sort(B + 1, B + tot3 + 1);
	stable_sort(P + 1, P + tot2 + 1);
	
//	printf("%d %d\n", tot3, tot2);
	
	if (tot3 < tot2) return false;
	for(; tot3 && tot2; --tot3, --tot2)
		if (B[tot3].left < P[tot2].dis) return false;
	return true;
}

int main() {
	freopen("a.in", "r", stdin);
	n = in();
	int u, v, w;
	for(int i = 1; i < n; ++i) {
		u = in(); v = in(); w = in();
		ins(u, v, w);
		ins(v, u, w);
	}
	
	dfs(1);
	for(int j = 1; j <= 17; ++j)
		for(int i = 1; i <= n; ++i) {
			f[i][j] = f[f[i][j - 1]][j - 1];
			if (f[i][j]) c[i][j] = c[i][j - 1] + c[f[i][j - 1]][j - 1];
		}
	m = in();
	for(int i = 1; i <= m; ++i) Army[i] = in();
	ll left = 0, right = 50000000000000ll, mid;
	while (left < right) {
		mid = (left + right) >> 1;
		if (can(mid)) right = mid;
		else left = mid + 1;
	}
	
	printf("%lld\n", left);
	return 0;
}

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