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Author: BrandonTang89

Other_Tasks/CF2060_E_Graph_Composition.cpp

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+#pragma GCC optimize("Ofast")
+#pragma GCC optimize("unroll-loops")
+#include <bits/stdc++.h>  
+using namespace std;
+
+int n, e, e2;
+vector<vector<int>> adjlist;
+vector<vector<int>> adjlistg;
+vector<int> colour;
+
+void dfs(int u, int col){
+    colour[u] = col;
+    for (int v : adjlistg[u]){
+        if (colour[v] == -1){
+            dfs(v, col);
+        }
+    }
+}
+
+vector<int> colour2;
+void dfs2(int u, int col){
+    colour2[u] = col;
+    for (int v : adjlist[u]){
+        if (colour2[v] == -1){
+            dfs2(v, col);
+        }
+    }
+}
+
+int main(){
+    int tc;
+    cin >> tc;
+    while(tc--){
+        cin >> n >> e >> e2;
+        adjlist.assign(n, vector<int>());
+        adjlistg.assign(n, vector<int>());
+        colour.assign(n, -1);
+
+        vector<pair<int, int>> el(e);
+        for (int i=0; i<e; i++){
+            int a, b;
+            cin >> a >> b;
+            a--; b--;
+            el[i] = {a, b};
+        }
+
+        for (int i=0; i<e2; i++){
+            int a, b;
+            cin >> a >> b;
+            a--; b--;
+            adjlistg[a].push_back(b);
+            adjlistg[b].push_back(a);
+        }
+
+
+        // colour nodes based on G
+        int col = 0;
+        for (int i=0; i<n; i++){
+            if (colour[i] == -1){
+                dfs(i, col);
+                col++;
+            }
+        }
+
+        // remove edges across colours in F
+        // vector<pair<int, int>> reducedel;
+        int ans = 0;
+        for (auto [a, b] : el){
+            if (colour[a] == colour[b]){
+                adjlist[a].push_back(b);
+                adjlist[b].push_back(a);
+            }
+            else{
+                ans++;
+            }
+        }
+
+        // colour nodes based on F
+        colour2.assign(n, -1);
+        int col2 = 0;
+        for (int i=0; i<n; i++){
+            if (colour2[i] == -1){
+                dfs2(i, col2);
+                col2++;
+            }
+        }
+
+        ans += col2 - col;
+        cout << ans << endl;
+    }
+
+    return 0;
+}