【BZOJ 1061】【Vijos 1825】【NOI 2008】志愿者招募

http://www.lydsy.com/JudgeOnline/problem.php?id=1061
https://vijos.org/p/1825
直接上姜爷论文。。。

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
typedef long long ll;
const int N = 1013;
const int M = 40003;
const int inf = 0x7fffffff;

struct node {int nxt, to, c, w, from;} E[M];
int cnt = 1, point[N << 1];

void ins(int u, int v, int c, int w) {
	E[++cnt] = (node) {point[u], v, c, w, u}; point[u] = cnt;
	E[++cnt] = (node) {point[v], u, 0, -w, v}; point[v] = cnt;
}

bool inq[N];
int dist[N], pre[N], q[N];

bool spfa(int s, int t) {
	for (int i = s; i <= t; ++i) dist[i] = inf, pre[i] = 0;
	int u, v, tt, head = 0, tail = 1; q[1] = s; inq[s] = true; dist[s] = 0;
	while (head != tail) {
		++head; if (head == N) head = 0;
		u = q[head]; inq[u] = false;
		for (int i = point[u]; i; i = E[i].nxt)
			if (E[i].c && dist[v = E[i].to] > (tt = dist[u] + E[i].w)) {
				dist[v] = tt; pre[v] = i;
				if (!inq[v]) {
					inq[v] = true;
					++tail; if (tail == N) tail = 0;
					q[tail] = v;
				}
			}
	}
	return dist[t] != inf;
}

ll MCMF(int s, int t) {
	ll ret = 0;
	while (spfa(s, t)) {
		int f = inf;
		for (int u = t; u != s; u = E[pre[u]].from) f = min(f, E[pre[u]].c);
		for (int u = t; u != s; u = E[pre[u]].from) E[pre[u]].c -= f, E[pre[u] ^ 1].c += f;
		ret += f * dist[t];
	}
	return ret;
}

int n, m, s, t, c, S, T, a[N];

int main() {
	scanf("%d%d", &n, &m);
	S = 0; T = n + 2;
	for (int i = 1; i <= n; ++i) scanf("%d", a + i);
	for (int i = 0; i <= n; ++i) {
		int num = a[i + 1] - a[i];
		if (num < 0) ins(i + 1, T, -num, 0);
		if (num > 0) ins(S, i + 1, num, 0);
	}
	for (int i = 1; i <= n; ++i) ins(i + 1, i, inf, 0);
	for (int i = 1; i <= m; ++i) {
		scanf("%d%d%d", &s, &t, &c);
		ins(s, t + 1, inf, c);
	}
	
	printf("%lld\n", MCMF(S, T));
	return 0;
}