Create Tree to Prufer code.cpp

Author: XDoodler

Tree to Prufer code.cpp

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+/*
+  Tree to Prufer Code
+  Complexity: O(VlogV)
+ */
+
+vector<int> treeToPrufercode (int nodes, vector<pair<int,int>> &edges) {
+    unordered_set<int> neighbors[nodes+1]; // For each node, who is it's neighbor?
+
+    for( int i = 0; i < edges.size(); i++ ) {
+        pair<int,int> edge = edges[i];
+        int u = edges[i].first; int v = edges[i].second;
+        neighbors[u].insert(v);
+        neighbors[v].insert(u);
+    }
+
+    priority_queue<int> leaves;
+    for ( int i = 0; i <= nodes; i++ ) {
+        if (neighbors[i].size() == 1 ) {
+            leaves.push(-i); // Negating since we need min heap
+        }
+    }
+    vector<int> pruferCode;
+    int need = nodes - 2;
+    while(need--) {
+        int leaf = -leaves.top(); leaves.pop();
+        int neighborOfLeaf = *(neighbors[leaf].begin());
+        pruferCode.push_back(neighborOfLeaf);
+        // Remove the leaf
+        neighbors[neighborOfLeaf].erase(leaf);
+        // The neighbor can become a new leaf
+        if(neighbors[neighborOfLeaf].size() == 1) {
+            leaves.push(-neighborOfLeaf);
+        }
+    }
+    return pruferCode;
+}