Tree Left View

Author: akashmodak97

Hacker Blocks/Tree Left View.cpp

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+/* Hacker Blocks */
+/* Title - Tree Left View */
+/* Created By - Akash Modak */
+/* Date - 26/10/2020 */
+
+// Given a binary tree , print its nodes from root to bottom as visible from left side of tree
+
+// Input Format
+// Level order input for the binary tree will be given.
+
+// Constraints
+// No of nodes in the tree can be less than or equal to 10^7
+
+// Output Format
+// A single line containing space separated integers representing the left view of the tree
+
+// Sample Input
+// 1 2 3 4 5 -1 6 -1 -1 -1 -1 -1 -1
+// Sample Output
+// 1 2 4
+// Explanation
+// The tree looks like
+
+//              1
+//           /      \
+//        2           3
+//     /     \           \
+//    4       5           6
+// When viewed from the left , we would see the nodes 1,2 and 4.
+
+#include<bits/stdc++.h>
+using namespace std;
+class node{
+	public: int data;
+	node* left,*right;
+	node(int d){
+		data = d;
+		left = right = NULL;
+	}
+};
+
+void leftView(node* root){
+	queue<node*> q;
+	q.push(root);
+	while(!q.empty()){
+		int n = q.size();
+		for(int i=0;i<n;i++){
+			node* temp = q.front();
+			q.pop();
+			if(i==0)
+			cout<<temp->data<<" ";
+
+			if(temp->left)
+			q.push(temp->left);
+			if(temp->right)
+			q.push(temp->right);
+		}
+	}
+	return;
+}
+void leftViewRecur(node* root,int level,int *maxLevel){
+	if(root==NULL)
+	return;
+
+	if(*maxLevel<level){
+		cout<<root->data<<" ";
+		*maxLevel = level;
+	}
+	leftViewRecur(root->left,level+1,maxLevel);
+	leftViewRecur(root->right,level+1,maxLevel);
+}
+
+node* create(){
+	int d;
+	cin>>d;
+	if(d==-1)
+	return NULL;
+	node* root = new node(d);
+	queue<node*> q;
+	q.push(root);
+	while(!q.empty()){
+		node* temp = q.front();
+		q.pop();
+		cin>>d;
+		if(d!=-1){
+			temp->left = new node(d);
+			q.push(temp->left);
+		}
+		cin>>d;
+		if(d!=-1){
+			temp->right = new node(d);
+			q.push(temp->right);
+		}
+	}
+	return root;
+}
+int main() {
+	node* root = create();
+	leftView(root);
+	int m = 0;
+	// inorder(root); cout<<endl;
+	// leftViewRecur(root,1,&m);
+	return 0;
+}