Create left_view_of_binary_tree.cpp

Author: avidLearnerInProgress

left_view_of_binary_tree.cpp

@@ -0,0 +1,158 @@
+// { Driver Code Starts
+#include <bits/stdc++.h>
+using namespace std;
+
+// Tree Node
+struct Node
+{
+    int data;
+    Node* left;
+    Node* right;
+};
+
+vector<int> leftView(struct Node *root);
+
+// Utility function to create a new Tree Node
+Node* newNode(int val)
+{
+    Node* temp = new Node;
+    temp->data = val;
+    temp->left = NULL;
+    temp->right = NULL;
+
+    return temp;
+}
+
+
+// Function to Build Tree
+Node* buildTree(string str)
+{
+    // Corner Case
+    if(str.length() == 0 || str[0] == 'N')
+        return NULL;
+
+    // Creating vector of strings from input
+    // string after spliting by space
+    vector<string> ip;
+
+    istringstream iss(str);
+    for(string str; iss >> str; )
+        ip.push_back(str);
+
+    // for(string i:ip)
+    //     cout<<i<<" ";
+    // cout<<endl;
+    // Create the root of the tree
+    Node* root = newNode(stoi(ip[0]));
+
+    // Push the root to the queue
+    queue<Node*> queue;
+    queue.push(root);
+
+    // Starting from the second element
+    int i = 1;
+    while(!queue.empty() && i < ip.size()) {
+
+        // Get and remove the front of the queue
+        Node* currNode = queue.front();
+        queue.pop();
+
+        // Get the current node's value from the string
+        string currVal = ip[i];
+
+        // If the left child is not null
+        if(currVal != "N") {
+
+            // Create the left child for the current node
+            currNode->left = newNode(stoi(currVal));
+
+            // Push it to the queue
+            queue.push(currNode->left);
+        }
+
+        // For the right child
+        i++;
+        if(i >= ip.size())
+            break;
+        currVal = ip[i];
+
+        // If the right child is not null
+        if(currVal != "N") {
+
+            // Create the right child for the current node
+            currNode->right = newNode(stoi(currVal));
+
+            // Push it to the queue
+            queue.push(currNode->right);
+        }
+        i++;
+    }
+
+    return root;
+}
+
+
+int main() {
+    int t;
+    scanf("%d ",&t);
+    while(t--)
+    {
+        string s;
+        getline(cin,s);
+        Node* root = buildTree(s);
+        vector<int> vec = leftView(root);
+        for(int x : vec)
+        cout<<x<<" ";
+        cout << endl;
+    }
+    return 0;
+}
+
+// } Driver Code Ends
+
+
+/* A binary tree node
+
+struct Node
+{
+    int data;
+    struct Node* left;
+    struct Node* right;
+    
+    Node(int x){
+        data = x;
+        left = right = NULL;
+    }
+};
+ */
+
+//Function to return a list containing elements of left view of the binary tree.
+vector<int> leftView(Node *root)
+{
+    if(!root) return {};
+   // Your code here
+   vector<int> result;
+   queue<Node* > qu;
+   
+   qu.push(root);
+   
+   while(!qu.empty()) {
+       
+       int n = qu.size();
+       
+       for(int i = 0; i < n; i++) {
+            
+            
+            auto current = qu.front();
+            qu.pop();
+            
+            if(i == 0) result.push_back(current->data);
+            
+            if(current->left) 
+                qu.push(current->left);
+            if(current->right) 
+                qu.push(current->right);
+       }       
+   }
+   return result;
+}