POJ 3140 Contestants Division——树形dp

m的大小是哄人的，其实m恒等于n-1，然后就是很普通的树形dp了，注意用long long

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
typedef long long ll;
const ll INF = 1e12;
const int maxn = 1e5 + 10;

int n, m;
ll dp[maxn];
int tot, head[maxn];
struct Edge {
    int to, next;
}edge[maxn<<1];
void init() {
    tot = 0;
    memset(head, -1, sizeof(head));
}
void addedge(int u, int v) {
    ++tot;
    edge[tot].to = v, edge[tot].next = head[u];
    head[u] = tot;
}

void dfs(int u, int p) {
    for (int i = head[u]; i != -1; i = edge[i].next) {
        int v = edge[i].to;
        if (v == p) continue;
        dfs(v, u);
        dp[u] += dp[v];
    }
}

ll iabs(ll x) {
    return x >= 0 ? x : -x;
}

int main() {
    int flag = 0;
    while (~scanf("%d %d", &n, &m) && (n + m)) {
        if (m != n - 1) {
            for (int i = 1; ;i++);
        }
        init();
        int u, v;
        ll sum = 0;
        for (int i = 1; i <= n; i++) {
            scanf("%lld", &dp[i]);
            sum += dp[i];
        }
        for (int i = 1; i <= m; i++) {
            scanf("%d %d", &u, &v);
            addedge(u, v); addedge(v, u);
        }
        dfs(1, -1);
//        for (int i = 1; i <= n; i++) cout << dp[i] << " ";
//        cout << endl;
        ll ans = INF;
        for (int i = 1; i <= n; i++) {
            ll a = dp[i], b = sum - dp[i];
            ans = min(ans, iabs(a - b));
        }
        printf("Case %d: %lld\n", ++flag, ans);
    }
    return 0;
}