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  • 【luogu P1262 间谍网络】 题解

    题目链接:https://www.luogu.org/problemnew/show/P1262
    注意:
    1.缩点时计算出入度是在缩完点的图上用color计算。不要在原来的点上计算。
    2.枚举出入度时是在缩完点的图上计算。枚举范围到num。

    #include <stack>
    #include <cstdio>
    #include <cstring>
    #include <iostream>
    #include <algorithm>
    using namespace std;
    const int maxn = 10000 + 10;
    struct edge{
    	int from, next, to, len;
    }e[maxn<<2];
    int head[maxn], cnt;
    int dfn[maxn], low[maxn], tim, color[maxn], num, rudu[maxn];
    stack<int> s;
    bool vis[maxn], okbuy[maxn], flag[maxn];
    int n, p, m, money[maxn], minpay[maxn], ans;
    void add(int u, int v)
    {
    	e[++cnt].from = u;
    	e[cnt].next = head[u];
    	e[cnt].to = v;
    	head[u] = cnt;
    }
    void tarjan(int x)
    {
    	dfn[x] = low[x] = ++tim;
    	s.push(x); vis[x] = 1;
    	for(int i = head[x]; i != -1; i = e[i].next)
    	{
    		int v = e[i].to;
    		if(!dfn[v])
    		{
    			tarjan(v);
    			low[x] = min(low[x], low[v]);
    		}
    		else if(vis[v])
    		{
    			low[x] = min(low[x], low[v]);
    		}
    	}
    	if(low[x] == dfn[x])
    	{
    		color[x] = ++num;
    		vis[x] = 0;
    		minpay[num] = min(minpay[num], money[x]);
    		while(s.top() != x)
    		{
    			color[s.top()] = num;
    			vis[s.top()] = 0;
    			minpay[num] = min(minpay[num], money[s.top()]);
    			s.pop();
    		}
    		s.pop();
    	}
    }
    int main()
    {
    	memset(head, -1, sizeof(head));
    	scanf("%d%d",&n,&p);
    	for(int i = 1; i <= n; i++) minpay[i] = 0x7fffffff, money[i] = 0x7fffffff;
    	for(int i = 1; i <= p; i++)
    	{
    		int u, val;
    		scanf("%d%d",&u,&val);
    		okbuy[u] = 1;
    		money[u] = val;
    	}
    	scanf("%d",&m);
    	for(int i = 1; i <= m; i++)
    	{
    		int u, v;
    		scanf("%d%d",&u,&v);
    		add(u,v);
    	}
    	for(int i = 1; i <= n; i++)
    		if(!dfn[i] && okbuy[i] == 1) tarjan(i);
    	for(int i = 1; i <= n; i++)
    		if(!dfn[i])
    		{
    			printf("NO
    %d",i);
    			return 0;
    		}
    	for(int i = 1; i <= n; i++)
    		for(int j = head[i]; j != -1; j = e[j].next)
    		{
    			int v = e[j].to;
    			if(color[v] != color[i])
    			{
    				rudu[color[v]]++;
    			}
    		}	
    	for(int i = 1; i <= num; i++)
    	{
    		if(rudu[i] == 0)
    		ans += minpay[i];
    	}
    	printf("YES
    %d
    ",ans);
    	return 0;	
    }
    
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  • 原文地址:https://www.cnblogs.com/MisakaAzusa/p/9374501.html
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