H - Line Graph Matching

https://codeforces.com/gym/103427/submission/143971438

Gym/103427/H/H.cpp

@@ -0,0 +1,68 @@
+#include <cstring>
+#include <iostream>
+
+using std::cin;
+using std::cout;
+using std::endl;
+
+const int N = 100005,
+          M = 200005;
+
+int n, m, min;
+long long ans;
+
+// Graph
+int idx, head[N], edge[M << 1], ver[M << 1], next[M << 1];
+
+void add(int u, int v, int w) {
+    next[idx] = head[u];
+    ver[idx] = v;
+    edge[idx] = w;
+    head[u] = idx++;
+}
+
+// Tarjan
+int cnt, dfn[N], low[N];
+int siz[N];
+
+void tarjan(int u, int in_edge) {
+    dfn[u] = low[u] = ++cnt;
+    for (int i = head[u]; ~i; i = next[i]) {
+        int v = ver[i];
+        if (!dfn[v]) {
+            tarjan(v, i);
+            siz[u] += siz[v] + 1;
+            low[u] = std::min(low[u], low[v]);
+            if (low[v] > dfn[u]) {
+                if (siz[v] % 2 == 0) {
+                    min = std::min(min, edge[i]);
+                }
+            } else {
+                min = std::min(min, edge[i]);
+            }
+        } else if (i != (in_edge ^ 1)) {
+            if (dfn[u] > dfn[v]) {
+                siz[u]++;
+            }
+            low[u] = std::min(low[u], dfn[v]);
+            min = std::min(min, edge[i]);
+        }
+    }
+}
+
+int main() {
+    memset(head, 0xff, sizeof(head));
+    cin >> n >> m;
+    for (int i = 1; i <= m; i++) {
+        int u, v, w;
+        cin >> u >> v >> w;
+        add(u, v, w);
+        add(v, u, w);
+        ans += w;
+    }
+    min = INT32_MAX;
+    tarjan(1, 0);
+    if (m & 1) ans -= min;
+    cout << ans << endl;
+    return 0;
+}