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Bottom_to_Top.cpp
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Bottom_to_Top.cpp
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#include<iostream>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;
class Node{
public:
int data;
Node* left;
Node* right;
Node(int val)
{
data = val;
left = NULL;
right = NULL;
}
};
void printBT(const std::string& prefix, const Node* node, bool isLeft)
{
if (node != nullptr)
{
std::cout << prefix;
std::cout << (isLeft ? "|--" : "L--");
std::cout << node->data << std::endl;
printBT(prefix + (isLeft ? "| " : " "), node->right, true);
printBT(prefix + (isLeft ? "| " : " "), node->left, false);
}
}
void printBT(const Node* node)
{
printBT("", node, false);
}
// Leetcode : 107.
/*
Level Order traversal of a BT from bottom to up.
Input: root = [3,9,20,null,null,15,7]
Output: [[15,7],[9,20],[3]]
*/
vector<vector<int>> levelOrderBottom(Node* root) {
vector<vector<int>> ans;
if(root==NULL)
return ans;
queue<Node*> q;
q.push(root);
while(!q.empty())
{
int size = q.size();
vector<int> temp;
for(int i=0; i<size; i++)
{
Node* frontnode = q.front();
q.pop();
temp.push_back(frontnode->data);
if(frontnode->left)
q.push(frontnode->left);
if(frontnode->right)
q.push(frontnode->right);
}
ans.push_back(temp);
temp.clear();
}
reverse(ans.begin(), ans.end());
return ans;
}
int main()
{
Node* root = new Node(1);
root->left = new Node(2);
root->right = new Node(3);
return 0;
}