ZOJ Problem Set - 2676 Network Wars

#include <utility>
#include <algorithm>
#include <string>
#include <cstring>
#include <cstdio>
#include <iostream>
#include <iomanip>
#include <set>
#include <vector>
#include <cmath>
#include <queue>
#include <bitset>
#include <map>
#include <iterator>
using namespace std;
#define clr(a,v) memset(a,v,sizeof(a))
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
const int INF = 0x7f7f7f7f;
const int maxn = 411;
const double pi = acos(-1.0);
const double eps = 1e-8;
const int mod = 777777777;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int, int> pii;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<VVI> VVVI;
struct node {
	int v, next;
	double w;
	node() {
	}
	node(int v, int next, double w) :
			v(v), next(next), w(w) {
	}
} edge[211111];
double dblcmp(double x) {
	if (x < -eps)
		return -1;
	return x > eps;
}

int E, head[maxn], n, dis[maxn], cur[maxn], pre[maxn], gap[maxn];
bool vis[maxn];
int cut[maxn], cnt;
template<typename T>
T minx(T a, T b) {
	return (a == -1 || b < a) ? b : a;
}
void init() {
	E = 0;
	clr(head, -1);
}
void add_edge(int u, int v, double c, double r) {
	edge[E] = node(v, head[u], c - r);
	head[u] = E++;
	edge[E] = node(u, head[v], 0);
	head[v] = E++;
}
double sap(int s, int t, int n) {
	int i;
	clr(gap, 0);
	clr(dis, 0);
	gap[0] = n;
	for (i = 0; i <= n; ++i)
		cur[i] = head[i];
	int u = pre[s] = s, v;
	double maxflow = 0, aug = -1;
	while (dis[s] < n) {
		loop: for (i = cur[u]; ~i; i = edge[i].next) {
			v = edge[i].v;
			if (dblcmp(edge[i].w) > 0 && dis[u] == dis[v] + 1) {
				aug = minx(aug, edge[i].w);
				cur[u] = i;
				pre[v] = u;
				u = v;
				if (u == t) {
					for (u = pre[u]; v != s; v = u, u = pre[u]) {
						edge[cur[u]].w -= aug;
						edge[cur[u] ^ 1].w += aug;
					}
					maxflow += aug;
					aug = -1;
				}
				goto loop;
			}
		}
		int mindis = n;
		for (i = head[u]; ~i; i = edge[i].next) {
			v = edge[i].v;
			if (dblcmp(edge[i].w) > 0 && mindis > dis[v]) {
				mindis = dis[v];
				cur[u] = i;
			}
		}
		if ((--gap[dis[u]]) == 0)
			break;
		gap[dis[u] = mindis + 1]++;
		u = pre[u];
	}
	return maxflow;
}
double c[maxn<<2];
void dfs(int u) {
	vis[u] = true;
	int i, v;
	for (i = head[u]; ~i; i = edge[i].next) {
		v = edge[i].v;
		if (vis[v])
			continue;
		if (dblcmp(edge[i].w) > 0) {
			dfs(v);
		}
	}
}
double MinCut() {
	clr(vis, false);
	cnt = 0;
	dfs(1);
	double w = 0;
	for (int i = 0; i < cnt; i += 2)
		w += c[cut[i] << 1];
	return w * 1.0 / cnt;
}
int u[maxn<<2], v[maxn<<2];
int main() {
	ios::sync_with_stdio(false);
	int n, m, i;
	while (~scanf("%d%d", &n, &m)) {
		init();
		for (i = 0; i < m; ++i) {
			scanf("%d%d%lf", u + i, v + i, c + i);
			add_edge(u[i], v[i], c[i], 0);
		}
		//double r = sap(1, n, n);
		double l, r, mid;
		l = 0, r = 1e7;
		double res = 0;
		while (r - l > eps) {
			mid = (l + r) * 0.5;
			init();
			res = 0;
			for (i = 0; i < m; ++i) {
				add_edge(u[i], v[i], c[i], mid);
				add_edge(v[i], u[i], c[i], mid);
				if (c[i] - mid < 0)
					res += c[i] - mid;
			}
			res += sap(1, n, n);
			if (dblcmp(res) < 0)
				r = mid;
			else
				l = mid;
		}
		cnt = 0;
		init();
		for (i = 0; i < m; ++i) {
			add_edge(u[i], v[i], c[i], mid);
			add_edge(v[i], u[i], c[i], mid);
			if (c[i] - mid < 0) {
				res += c[i] - mid;
				cut[cnt++] = i + 1;
			}
		}
		res += sap(1, n, n);
		clr(vis, false);
		dfs(1);
		for (i = 0; i < E; ++i) {
			if (vis[edge[i].v] ^ vis[edge[i ^ 1].v])
				cut[cnt++] = (i >> 2) + 1;
		}
		sort(cut, cut + cnt);
		cnt = unique(cut, cut + cnt) - cut;
		printf("%d\n", cnt);
		for (i = 0; i < cnt; ++i) {
			printf("%d%c", cut[i], i == cnt - 1 ? '\n' : ' ');
		}
	}
	return 0;
}