rt

我使用的是 vector+map 存边，故代码比较晦涩，我自己也难以驾驭，实在调不出，求助。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <map>

using namespace std;

const long long INF = 2147483647;

long long N,M,Root,Goal;
vector<long long> Edge[33];
map<long long,long long> Mp[33];
long long Pre[33],W[33],D[33],H[33]; 
vector<long long>::iterator P[33];

vector<long long>::iterator Adv;
long long Min;
long long First,End;
long long Value;
long long Flow;
bool Flag;

long long i;

long long Answer;

void MakeEdge(long long L1,long long L2,long long Value)
{
	Edge[L1].push_back(L2);
	if(Mp[L1].find(L2) == Mp[L1].end())
		Mp[L1].insert({L2,Value});
	else
		Mp[L1][L2] += Value; 
	return ;
}

int main()
{
	scanf("%lld%lld%lld%lld",&N,&M,&Root,&Goal);
	for(i = 1 ; i<= M ; i++)
	{
		scanf("%lld%lld%lld",&First,&End,&Value);
		MakeEdge(First,End,Value);
		MakeEdge(End,First,0);
	}
	for(i = 1 ; i<= N ; i++)
		D[i] = 0,P[i] = Edge[i].begin();
	H[0] = N;
	i = Root;
	Flow = INF;
	while(D[Root] < N)
	{
		W[i] = Flow;
		Flag = false;
		for(vector<long long>::iterator it = P[i] ; it != Edge[i].end() ; it++)
        //仅仅P[i](即当前弧优化)有问题，如果将 P[i] 改成 Edge[i].begin() ，是可以 AC 的。
		{
			if(Mp[i][*it] == 0 || D[*it] != D[i]-1 )
				continue;
			Flag = true;
			P[i] = it;
			Flow = min(Flow,Mp[i][*it]);
			Pre[*it] = i;
			i = *it;
			if(i == Goal)
			{
				Answer += Flow;
				while(i != Root)
				{
					cout << i << endl;
					Mp[i][Pre[i]] += Flow;
					Mp[Pre[i]][i] -= Flow;
					i = Pre[i];
				}
				Flow = INF;
				
			}
			break;
		}
		if(Flag) continue;
		Min = N-1;
		Adv = Edge[i].begin(); 
		for(vector<long long>::iterator it = Edge[i].begin() ; it != Edge[i].end() ; it++)
		{
			if(Mp[i][*it] != 0 && D[*it] < Min)
			{
				Min = D[*it];
				Adv = it;
			}
		}
		H[D[i]]--;
		if(H[D[i]] == 0)
			break;
		D[i] = Min+1;
		H[D[i]]++;
		if(i != Root)
		{
			i = Pre[i];
			Flow = W[i];
		}
	}
	printf("%lld\n",Answer);
	return 0;
}