Trees and Graph

Author: dexterrxx31

Graph_adjacency_list.cpp

@@ -0,0 +1,50 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Graph
+{
+    int v;
+    list<int> *l;
+
+public:
+    Graph(int v)
+    {
+        this->v = v;
+        l = new list<int>[v];
+    }
+    void addEdge(int x, int y)
+    {
+        l[x].push_back(y);
+        l[y].push_back(x);
+    }
+
+    void printAdjList()
+    {
+        for (int i = 0; i < v; i++)
+        {
+            cout << "Vertex " << i << "->";
+            for (int nbr : l[i])
+            {
+                cout << nbr << ",";
+            }
+            cout << endl;
+        }
+    }
+};
+
+int main()
+{
+#ifndef ONLINE_JUDGE
+    freopen("input.txt", "r", stdin);
+    freopen("output.txt", "w", stdout);
+#endif
+
+    Graph g(4);
+    g.addEdge(0, 1);
+    g.addEdge(0, 2);
+    g.addEdge(2, 3);
+    g.addEdge(1, 2);
+
+    g.printAdjList();
+    return 0;
+}

level_order_traversal_trees.cpp

@@ -0,0 +1,40 @@
+class Solution {
+public:
+    //We need to apply Breadth first Search for this given tree.
+    // That is why we need a Queue for DS for our problem .
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        if (!root) return {}; // if Tree is Empty
+        vector<vector<int>> ans;
+        
+        // We are taking Queue to do Level Order Traversal
+        queue<TreeNode*>q ;
+        q.push(root);
+        
+        // We are suppose to set some indication for one level to end , here we chose NULL
+        q.push(NULL);
+        vector<int> temp ; // vector to keep current array of items
+        while(!q.empty())
+        {   
+            TreeNode *ptr = q.front();
+            q.pop(); // Removing front item and will be adding children for same front element
+            //Check for Level Order and push current vector to main answer.
+            if(ptr == NULL)
+            {
+                ans.push_back(temp);
+                temp.clear();
+                if(!q.empty()) q.push(NULL); // check if atleast one parent element left in queue.
+            }
+            else
+            {
+                temp.push_back(ptr->val);
+                
+                // pushing childens of current front element.
+                if(ptr->left) q.push(ptr->left);
+                if(ptr->right) q.push(ptr->right);
+            }
+            
+        }
+        
+        return ans;
+    }
+};