Print Binary Tree levels in sorted order | Set 3 (Tree given as array)

Given a Complete Binary Tree as an array, the task is to print all of its levels in sorted order.

Examples:

Input: arr[] = {7, 6, 5, 4, 3, 2, 1}
The given tree looks like
            7
          /   \
        6      5
       / \    / \
      4  3   2   1
Output:
7
5 6
1 2 3 4

Input: arr[] = {5, 6, 4, 9, 2, 1}
The given tree looks like 
            5
          /   \
        6      4
       / \    /    
      9   2  1
Output: 
5
4 6
1 2 9

Approach: A similar problem is discussed here
As the given tree is a Complete Binary Tree:

No. of nodes at a level l will be 2l where l ≥ 0
  1. Start traversing the array with level initialized as 0.
  2. Sort the elements which are the part of the current level and print the elements.

Below is the implementation of the above approach:

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// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to print all the levels
// of the given tree in sorted order
void printSortedLevels(int arr[], int n)
{
  
    // Initialize level with 0
    int level = 0;
    for (int i = 0; i < n; level++) {
  
        // Number of nodes at current level
        int cnt = (int)pow(2, level);
  
        // Indexing of array starts from 0
        // so subtract no. of nodes by 1
        cnt -= 1;
  
        // Index of the last node in the current level
        int j = min(i + cnt, n - 1);
  
        // Sort the nodes of the current level
        sort(arr + i, arr + j + 1);
  
        // Print the sorted nodes
        while (i <= j) {
            cout << arr[i] << " ";
            i++;
        }
        cout << endl;
    }
}
  
// Driver code
int main()
{
    int arr[] = { 5, 6, 4, 9, 2, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);
    printSortedLevels(arr, n);
  
    return 0;
}

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Output:

5 
4 6 
1 2 9


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