2019 ACM-ICPC 西安邀请赛 D. Miku and Generals（并查集+dp）

【题目】

Miku and Generals

【代码】

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn=1000005;
int a[maxn],f[maxn];;
int dp[maxn],sum[maxn];
int pre[maxn],vis[maxn];
int l[maxn],r[maxn];
int Find(int x){return x==pre[x]?x:pre[x]=Find(pre[x]);}
void join(int x,int y)
{
    int fx=Find(x),fy=Find(y);
    if(fx!=fy) pre[fx]=fy;
}
int main()
{
	int t; scanf("%d",&t);
    while(t--){
        int qum=0;
        int n,m; scanf("%d%d",&n,&m);
        for(int i=1;i<=n;i++)
        {
            scanf("%d",&a[i]);
            a[i] /= 100;
            qum += a[i];
            sum[i]=a[i];
            pre[i]=i;
            vis[i]=0;
        }
		int x,y;
		for(int i=1;i<=m;i++)
		{
            for(int j=1;j<=n;j++)
                vis[j]=Find(vis[Find(j)]);
			scanf("%d%d",&x,&y);
            if(vis[Find(x)]==0&&vis[Find(y)]==0)
            {
                vis[Find(y)]=x;
                vis[Find(x)]=y;
            }
            else if(Find(vis[Find(x)])==0)
            {
                sum[Find(vis[Find(y)])]+=sum[Find(x)];
                join(Find(x),Find(vis[Find(y)]));
                vis[Find(x)]=Find(y);
            }
            else if(Find(vis[Find(y)])==0)
            {
                sum[Find(vis[Find(x)])]+=sum[Find(y)];
                join(Find(y),Find(vis[Find(x)]));
                vis[Find(y)]=Find(x);
            }
            else if(Find(y)!=Find(vis[Find(x)]))
            {
                sum[Find(x)]+=sum[Find(vis[Find(y)])];
                join(Find(vis[Find(y)]),Find(x));
                sum[Find(y)]+=sum[Find(vis[Find(x)])];
                join(Find(vis[Find(x)]),Find(y));
                    vis[Find(x)]=Find(y);
                    vis[Find(y)]=Find(x);
            }
		}
		int q=0;
        for(int j=1;j<=n;j++)
            vis[j]=Find(vis[Find(j)]);
		for(int i=1;i<=n;i++)
		{
			if(sum[Find(i)]==0&&sum[Find(vis[Find(i)])]==0)
				continue;
			else if(vis[i]!=0){
				q++;
				l[q]=sum[Find(i)],r[q]=sum[Find(vis[Find(i)])];
				sum[Find(i)]=0,sum[Find(vis[Find(i)])]=0;
			}
		}
		int ssum=0;
		for(int i=1;i<=q;i++){
			ssum+=min(l[i],r[i]);
			dp[i]=abs(l[i]-r[i]);
		}
		for(int i=1;i<=n;i++){
			if(vis[i]==0) dp[++q]=a[i];
		}
		memset(f,0,sizeof(f));
		f[ssum]=1;
		for(int i=1;i<=q;++i)
            for(int j=qum/2;j>=dp[i];--j)
                if(f[j-dp[i]]) f[j] = 1;
		ll ans=0;
		for(int i=qum/2;i>=0;--i)
            if(f[i]){
                ans=max(i*(ll)100,(qum-i)*(ll)100);
                break;
            }
		printf("%lld\n",ans);
	}
	return 0;
 }