ref – https://www.programiz.com/dsa/complete-binary-tree

A complete binary tree is when all nodes are filled, and the leaves are filled from the left.

A full tree is where each node has 0 or 2 children.

A complete binary tree has an interesting property that we can use to find the children and parents of any node.

If the index of any element in the array is i, the element in the index 2i+1 will become the left child and element in 2i+2 index will become the right child. Also, the parent of any element at index i is given by the lower bound of (i-1)/2.