POJ 2553 The Bottom of a Graph

最新推荐文章于 2019-10-06 08:14:21 发布

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最新推荐文章于 2019-10-06 08:14:21 发布

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原文链接：http://www.cnblogs.com/crisxyj/archive/2013/02/27/2935416.html

版权

Link: http://poj.org/problem?id=2553

求缩点后出度为0的点。。。 tarjan again。。。

首次用了memcpy方法感觉不错！

注意init()要在输入了 m n之后调用，一般来说上轮case里数组是 a[i] ++形式的要再次赋初值

而有变量cnt控制数组大小的数组不必赋值只要控制cnt=0 就可以了

如for(int i=1; i<=cnt; i++) a[i]=xxxx; 这类

View Code

#include <cstdio>
#include <iostream>
#include <stack>
#include <algorithm>
using std::stack;
using std::sort;

const int maxn = 5005, INF = (1<<30);
bool vis[maxn], inStack[maxn];
int dfn[maxn], low[maxn], belong[maxn], size[maxn], m, n, round, cnt;
int out[maxn], arr[maxn][maxn];
int ans[maxn];
struct node
{
    int index;
    node *next;
}edge[maxn];
stack<int> s;
int min(int a, int b)
{
    return a<=b ?a :b ;
}
void tarjan(int u)
{
    int i;
    dfn[u] = low[u] = round ++ ;
    vis[u] = 1;
    inStack[u] = 1;
    s.push(u);
    node *p = edge[u].next;
    while( p != NULL )
    {
        int v = p->index;
        if( !vis[v] )
        {
            tarjan(v);
            low[u] = min(low[u], low[v]);
        }
        else if( inStack[v] )
            low[u] = min(low[u], dfn[v]);
        p = p->next;
    }
    if( low[u] == dfn[u] )
    {
        cnt ++;
        while(i = s.top())
        {
            size[cnt] ++;
            arr[cnt][size[cnt]] = i;
            belong[i] = cnt;
            inStack[i] = 0;
            s.pop();
            if( i==u )
                break;
        }
    }
}
void init()
{
    cnt = 0;
    memset(ans, 0, sizeof(ans));
    memset(vis, 0, sizeof(vis));
    memset(out, 0, sizeof(out));
    memset(size, 0, sizeof(size));
    memset(inStack, 0, sizeof(inStack));
    for(int i=1; i<=n; i++)
    {
        edge[i].index = i;
        edge[i].next = NULL;
    }
}
int check()
{
    for(int i=1; i<=n; i++)
        if( !vis[i] )
            return i;
    return 0;
}
int main()
{
    int i, a, b;
    while(scanf("%d", &n), n!=0)
    {
        scanf("%d", &m);
        init();
        for(i=1; i<=m; i++)
        {
            scanf("%d %d", &a, &b);
            if( a == b )
                continue;
            node *p = (node *)malloc(sizeof(node));
            p->index = b;
            p->next = edge[a].next;
            edge[a].next = p;
        }
        while( i=check() )
            tarjan(i);
        for(i=1; i<=n; i++)
        {
            node *p = edge[i].next;
            while( p != NULL )
            {
                if( belong[i] != belong[p->index])
                    out[belong[i]]++ ;
                p = p->next;
            }
        }
        int minNum = INF, ansCnt = 0;
        for(i=1; i<=cnt; i++)
        {
            if(out[i] == 0)
            {
                memcpy(ans+ansCnt, arr[i]+1, sizeof(int)*size[i]);
                ansCnt += size[i];
            }
        }
        sort( ans, ans+ansCnt );
        for(i=0; i<ansCnt-1; i++)
            printf("%d ", ans[i]);
        printf("%d\n", ans[i]);
    }
    return 0;
}

转载于:https://www.cnblogs.com/crisxyj/archive/2013/02/27/2935416.html