HUD5438

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HUD 5438 Ponds

Solution Sketch

Key: Use DFS and yank nodes with $total\ degree = 1$

AC Code

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#include <cstdio>
#include <cstring>
#include <queue>
#include <vector>
using namespace std;
typedef long long ll;
#define N 11111
vector<int> g[N];
int deg[N], val[N];
queue<int> q;
void clear(int n)
{
    for (int i = 0; i <= n; i++)
        g[i].clear();
    memset(deg, 0, sizeof(deg));
}
void add_edge(int u, int v)
{
    g[u].push_back(v);
    g[v].push_back(u);
}
void dfs(int u)
{
    if (deg[u] == 1) {
        deg[u] = 0;
        for (int i = 0; i < (int)g[u].size(); i++) {
            int v = g[u][i];
            if (deg[v] > 0) {
                deg[v]--;
                dfs(v);
            }
        }
    } else {
        return;
    }
}
bool seen[N];
int cnt = 0;
ll total = 0;
void dfs1(int u)
{
    if (seen[u])
        return;
    seen[u] = true;
    cnt++;
    total += val[u];
    for (int i = 0; i < (int)g[u].size(); i++) {
        int v = g[u][i];
        if (deg[v] > 0) {
            dfs1(v);
        }
    }
}
int main()
{
    int ncase;
    scanf("%d", &ncase);
    while (ncase--) {
        int n, m;
        scanf("%d %d", &n, &m);
        clear(n);
        for (int i = 0; i < n; i++)
            scanf("%d", &val[i]);
        for (int i = 0; i < m; i++) {
            int u, v;
            scanf("%d %d", &u, &v);
            u--;
            v--;
            add_edge(u, v);
            deg[u]++;
            deg[v]++;
        }
        ll sum = 0;
        for (int i = 0; i < n; i++) {
            if (deg[i] == 1) // starter
                q.push(i);
        }
        while (q.empty() == false) {
            int u = q.front();
            q.pop();
            dfs(u);
        }
        memset(seen, false, sizeof(seen));
        for (int i = 0; i < n; i++) {
            if (deg[i] > 0 && seen[i] == false) {
                cnt = 0;
                total = 0;
                dfs1(i);
                if (cnt % 2 == 1 && cnt > 1)
                    sum += total;
            }
        }
        printf("%lld\n", sum);
    }
    return 0;
}