loj2042 「CQOI2016」不同的最小割

分治+最小割

看到题解的第一句话是这个就秒懂了，然后乱七八糟的错误、越界、RE……

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
#include <set>
using namespace std;
int n, m, uu, vv, ww, hea[855], cnt, a[855], ss, tt, lev[855], tmp[855], cur[855];
int maxFlow;
const int oo=0x3f3f3f3f;
queue<int> d;
set<int> se;
struct Edge{
	int too, nxt, val;
}edge[17005];
void add_edge(int fro, int too, int val){
	edge[cnt].nxt = hea[fro];
	edge[cnt].too = too;
	edge[cnt].val = val;
	hea[fro] = cnt++;
}
bool bfs(){
	memset(lev, 0, sizeof(lev));
	lev[ss] = 1;
	d.push(ss);
	while(!d.empty()){
		int x=d.front();
		d.pop();
		for(int i=hea[x]; i!=-1; i=edge[i].nxt){
			int t=edge[i].too;
			if(!lev[t] && edge[i].val>0){
				lev[t] = lev[x] + 1;
				d.push(t);
			}
		}
	}
	return lev[tt]!=0;
}
int dfs(int x, int lim){
	if(x==tt)	return lim;
	int addFlow=0;
	for(int &i=cur[x]; i!=-1; i=edge[i].nxt){
		int t=edge[i].too;
		if(lev[t]==lev[x]+1 && edge[i].val>0){
			int tmp=dfs(t, min(lim-addFlow, edge[i].val));
			edge[i].val -= tmp;
			edge[i^1].val += tmp;
			addFlow += tmp;
			if(addFlow>=lim)	break;
		}
	}
	return addFlow;
}
void dinic(){
	maxFlow = 0;
	while(bfs()){
		for(int i=1; i<=n; i++)
			cur[i] = hea[i];
		maxFlow += dfs(ss, oo);
	}
}
void solve(int l, int r){
	if(l>=r)	return ;
	for(int i=0; i<cnt; i+=2)
		edge[i].val = edge[i^1].val = (edge[i].val + edge[i^1].val) >> 1;
	ss = a[l]; tt = a[r];
	dinic();
	se.insert(maxFlow);
	int pu=l, pv=r;
	for(int i=l; i<=r; i++)
		if(lev[a[i]])
			tmp[pu++] = a[i];
		else
			tmp[pv--] = a[i];
	for(int i=l; i<=r; i++)
		a[i] = tmp[i];
	solve(l, pu-1);
	solve(pv+1, r);
}
int main(){
	memset(hea, -1, sizeof(hea));
	cin>>n>>m;
	for(int i=1; i<=m; i++){
		scanf("%d %d %d", &uu, &vv, &ww);
		add_edge(uu, vv, ww);
		add_edge(vv, uu, ww);
	}
	for(int i=1; i<=n; i++)
		a[i] = i;
	solve(1, n);
	cout<<se.size()<<endl;
	return 0;
}