【dp每一天】 POJ - 3140 Contestants Division (樹形dp)

這個故事告訴我們 long long的abs需要自己寫:)

說起來紫書上管這個點叫樹的重心?看來還get了重心的求法...

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;
#define ll long long
const int inf = 0x3f3f3f3f;
const int maxn = 1e5+20, maxe = 1e6+10;
int n,m;
struct node
{
    int to,next;
    node(){}
    node(int a,int b){to = a; next = b;}
}edge[maxe << 1];
int h[maxn],vis[maxn];
ll k[maxn];
ll sum[maxn];
int edgenum;
ll ans = 1e14,num;
void init()
{
    for(int i = 1; i <= n ; i++)
        h[i] = -1, k[i] = vis[i] = sum[i] = 0;
    edgenum = 0;    ans = 1e15;  num = 0;
}

void add(int f,int t)
{
    edge[edgenum] = node(t,h[f]);
    h[f] = edgenum++;
}
void solve(int u)
{
    sum[u] = k[u];
    for(int i = h[u] ;~i; i = edge[i].next)
    {
        int v = edge[i].to;
        if(vis[v]) continue;
        //cout <<"u v "<<u << " " << v << endl;
        vis[v] = 1;
        solve(v);
        sum[u] += sum[v];
    }
    ll th = num-sum[u]-sum[u] >= 0? num-sum[u]-sum[u]:(-(num-sum[u]-sum[u]));
    ans = min(ans,th);
}
int main()
{
    int kase = 1;int a,b;
    while(~scanf("%d%d",&n,&m) && n+m)
    {
        init();
        for(int i = 1; i <= n; i++)  {scanf("%lld",&k[i]);num += k[i];}
        //cout << num << endl;
        for(int i = 0; i < m ;i++)
        {
            scanf("%d%d",&a,&b);
            add(a,b); add(b,a);
        }

        vis[1] = 1;ans = num;
        solve(1);
        //for(int i = 1; i <= n ; i++)
        //    cout <<"i " << i << " " << sum[i] << endl;

        printf("Case %d: %lld\n",kase++,ans);
    }
    return 0;
}


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