hdu 5438 拓扑排序+并查集

remove的过程就像是拓扑排序，而最后统计sum可以用并查集，每个集合维护集合的size、sum。

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;

typedef long long ll;
const int INF = 999999999;
const int N = 20000;
const int M = 200000;
int f[N];
int sz[N];
ll sum[N];
int in[N];
int head[N];
queue<int> q;
int n, m, e;

struct Edge
{
    int v, next;
} edge[M << 1];

void addEdge( int u, int v )
{
    edge[e].v = v;
    edge[e].next = head[u];
    head[u] = e++;
}

void init()
{
    while ( !q.empty() ) q.pop();
    e = 0;
    memset( in, 0, sizeof(in) );
    memset( head, -1, sizeof(head) );
    for ( int i = 1; i <= n; i++ )
    {
        f[i] = i;
        sz[i] = 1;
    }
}

int findf( int x )
{
    if ( f[x] != x ) f[x] = findf( f[x] );
    return f[x];
}

void union_set( int x, int y )
{
    x = findf(x), y = findf(y);
    if ( x != y )
    {
        f[x] = y;
        sz[y] += sz[x];
        sum[y] += sum[x];
    }
}

int main ()
{
    int t;
    scanf("%d", &t);
    while ( t-- )
    {
        scanf("%d%d", &n, &m);
        init();
        for ( int i = 1; i <= n; i++ )
        {
            scanf("%I64d", &sum[i]);
        }
        while ( m-- )
        {
            int u, v;
            scanf("%d%d", &u, &v);
            in[u]++;
            in[v]++;
            addEdge( u, v );
            addEdge( v, u );
        }
        for ( int i = 1; i <= n; i++ )
        {
            if ( in[i] < 2 )
            {
                q.push(i);
                in[i] = INF;
            }
        }
        while ( !q.empty() )
        {
            int u = q.front();
            q.pop();
            for ( int i = head[u]; i != -1; i = edge[i].next )
            {
                int v = edge[i].v;
                in[v]--;
                if ( in[v] < 2 )
                {
                    q.push(v);
                    in[v] = INF;
                }
            }
        }
        for ( int i = 1; i <= n; i++ )
        {
            if ( in[i] > n ) continue;
            for ( int j = head[i]; j != -1; j = edge[j].next )
            {
                int v = edge[j].v;
                if ( in[v] > n ) continue;
                union_set( i, v );
            }
        }
        ll ans = 0;
        for ( int i = 1; i <= n; i++ )
        {
            if ( in[i] < n && f[i] == i && sz[i] % 2 == 1 )
            {
                ans += sum[i];
            }
        }
        printf("%I64d
", ans);
    }
    return 0;
}