How to determine if binary tree is balanced?

Question

It\'s been a while from those school years. Got a job as IT specialist at a hospital. Trying to move to do some actual programming now. I\'m working on binary trees now, a

Answer 1

Note 1: The height of any sub-tree is computed only once.

Note 2: If the left sub-tree is unbalanced then the computation of the right sub-tree, potentially containing million elements, is skipped.

// return height of tree rooted at "tn" if, and only if, it is a balanced subtree
// else return -1
int maxHeight( TreeNode const * tn ) {
    if( tn ) {
        int const lh = maxHeight( tn->left );
        if( lh == -1 ) return -1;
        int const rh = maxHeight( tn->right );
        if( rh == -1 ) return -1;
        if( abs( lh - rh ) > 1 ) return -1;
        return 1 + max( lh, rh );
    }
    return 0;
}

bool isBalanced( TreeNode const * root ) {
    // Unless the maxHeight is -1, the subtree under "root" is balanced
    return maxHeight( root ) != -1;
}