Create 310. Minimum Height Trees (#463)

Author: Chayandas07

310. Minimum Height Trees

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+
+class Solution {
+public:
+    vector<int> findMinHeightTrees(int n, vector<vector<int>>& edges) {
+        if(edges.size() == 0) {
+            vector<int> tmp;
+            tmp.push_back(0);
+            return tmp;
+        }
+        unordered_map<int, list<int>> adj;
+
+        // creating adjacency list
+        for (int i = 0; i < edges.size(); i++) {
+            int u = edges[i][0];
+            int v = edges[i][1];
+            adj[u].push_back(v);
+            adj[v].push_back(u);
+        }
+
+        vector<int> leaves; // Stores current leaf nodes
+
+        // Initialize leaves with nodes having only 1 adjacent node
+        for(auto& d : adj) {
+            if(d.second.size() == 1) {
+                leaves.push_back(d.first);
+            }
+        }
+
+        // answer can consist of max. 2 nodes (Reason explained above)
+        while(n > 2) {
+            vector<int> new_leaves;
+
+            // remove current leaves
+            n -= leaves.size(); 
+
+            for(int leaf : leaves) {
+                // get the only neighbour of leaf
+                int neighbor = adj[leaf].front(); 
+                // remove leaf from neighbour's adjacency list
+                adj[neighbor].remove(leaf); 
+                
+                // if the adjacent node becomes a leaf node after removal, add it to the queue.
+                if(adj[neighbor].size() == 1) {
+                    new_leaves.push_back(neighbor); 
+                }
+            }
+            
+            // update current no of leaf nodes
+            leaves = new_leaves; 
+        }
+
+        return leaves;
+    }
+};