Tree Top View

Author: akashmodak97

Hacker Blocks/Tree Top View.cpp

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+/* Hacker Blocks */
+/* Title - Tree Top View */
+/* Created By - Akash Modak */
+/* Date - 26/10/2020 */
+
+// Given a binary tree , print the nodes in left to right manner as visible from above the 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 top view of the tree
+
+// Sample Input
+// 1 2 3 4 5 6 -1 -1 -1 -1 -1 -1 -1
+// Sample Output
+// 4 2 1 3
+// Explanation
+// The tree looks like
+
+//              1
+//           /      \
+//        2           3
+//     /     \       /
+//    4       5     6
+// When viewed from the top , we would see the nodes 4, 2, 1 and 3.
+
+#include<bits/stdc++.h>
+using namespace std;
+class node{
+	public:
+	int data;
+	int hd;
+	node* left;
+	node* right;
+	node(int d){
+		data = d;
+		left=right=NULL;
+	}
+};
+
+node* build(){
+	int d;
+	cin>>d;
+	if(d==-1)
+	return NULL;
+	int hd = 0;
+	queue<node*> q;
+	node * root = new node(d);
+	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;
+}
+void topView(node* root){
+	queue<node*> q;
+	map<int,int> m;
+	int hd = 0;
+	root->hd = hd;
+	q.push(root);
+	while(!q.empty()){
+		node* temp = q.front();
+		q.pop();
+		hd = temp->hd;
+		if(m[hd]==0){
+			m[hd] = temp->data;
+		}
+		if(temp->left){
+			temp->left->hd = hd - 1;
+			q.push(temp->left);
+		}
+		if(temp->right){
+			temp->right->hd = hd+1;
+			q.push(temp->right);
+		}
+	}
+
+	for(auto x: m){
+		cout<<x.second<<" ";
+	}
+}
+
+int main() {
+	node * root = build();
+	topView(root);
+	return 0;
+}