白子的情人节礼物 题解

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#include<bits/stdc++.h>
#define int long long 
#define Blue_Archive return 0
#define con putchar(' ')
#define ent putchar('\n')
using namespace std;
constexpr int N = 5e5 + 7;
constexpr int M = 8e5 + 7;
constexpr int INF = 1e18;

int n;
int m;
int s;
int t;
int tot = 1;
int ans;
int a[N];
int b[N];
int c[N];
int h[N];
int w[M];
int to[M];
int nxt[M];
int dis[N];
int cur[N];

queue<int> q;

inline int read()
{
	int x = 0,k = 1;
	char op = getchar();
	while(op > '9' || op < '0')
	{
		if(op == '-') k = -1;
		op = getchar();
	} 
	while(op <= '9' && op >= '0') x = (x << 1) + (x << 3) + op - '0',op = getchar();
	return x * k;
}

inline void write(int x)
{
	if(x < 0) x = -x,putchar('-');
	if(x > 9) write(x / 10);
	putchar(x % 10 + '0');
}

inline void add(int a,int b,int c)
{
	to[++ tot] = b,w[tot] = c,nxt[tot] = h[a],h[a] = tot;
	to[++ tot] = a,w[tot] = 0,nxt[tot] = h[b],h[b] = tot;
}

inline bool bfs()
{
	for(int i = 1;i <= t;i ++) dis[i] = INF;
	queue<int> q;
	q.push(s);
	dis[s] = 0;
	cur[s] = h[s];
	while(!q.empty())
	{
		int u = q.front();
		q.pop();
		for(int i = h[u];i;i = nxt[i])
		{
			if(w[i] && dis[to[i]] == INF)
			{
				q.push(to[i]);
				cur[to[i]] = h[to[i]];
				dis[to[i]] = dis[u] + 1;
				if(to[i] == t) return 1;
			}
		}
	}
	return 0;
}

inline int dfs(int x,int sum)
{
	if(x == t) return sum;
	int k,res = 0;
	for(int i = cur[x];i && sum;i = nxt[i])
	{
		cur[x] = i;
		if(w[i] && dis[to[i]] == dis[x] + 1)
		{
			k = dfs(to[i],min(sum,w[i]));
			if(k == 0) dis[to[i]] = INF;
			w[i] -= k;
			w[i ^ 1] += k;
			res += k;
			sum -= k;
		}
	} 
	return res;
}

signed main()
{
	// freopen("data.in","r",stdin);freopen("data.out","w",stdout);
	n = read();
	m = read();
	s = n + 1;
	t = n + 2;
	for(int i = 1;i <= n;i ++) a[i] = read(),add(s,i,a[i]);
	for(int i = 1;i <= n;i ++) b[i] = read(),add(i,t,b[i]);
	for(int i = 1,u,v,w;i <= m;i ++)
	{
		u = read();
		v = read();
		w = read();
		add(u,v,w);
		add(v,u,w);
	}
	while(bfs()) ans += dfs(s,INF);
	write(ans);ent;
	Blue_Archive;
}