How to determine whether a binary tree is complete?

Question

A complete binary tree is defined as a binary tree in which every level, except possibly the deepest, is completely filled. At deepest level, all nodes must be as far left a

Answer 1

bool isComplete (struct Node* root){
    if(root==NULL)
    return true;                  // Recur for left and right subtree 
    bool flag=false;
    int option1=height(root->left);
    int option2=height(root->right);
    if(option1==option2||option1==option2+1)
    flag=true;
    return flag&&isComplete(root->left)&&isComplete(root->right);
    }

please consider as a correct answer if you found useful.

Answer 2

The simplest procedure is:

1. Find depth of the tree (simple algorithm).
2. Count the number of nodes in a tree (by traversing and increasing the counter by one on visiting any node).
3. For a complete binary tree of level d number of nodes equals to pow(2,d+1)-1.

If condition satisfy tree, is complete binary tree, else not.

That's a simple algorithm and turning it into a working code shouldn't be a problem if you are good enough coder.

Answer 3

You could combine three pieces of information from the subtrees:

• Whether the subtree is complete

• The maximal height

• The minimal height (equal to maximal height or to maximal height - 1)

Answer 4

private static boolean isCompleteBinaryTree(TreeNode root) {

if (root == null) {
    return false;
} else {
    boolean completeFlag = false;
    List<TreeNode> list = new ArrayList<TreeNode>();
    list.add(root);
    while (!list.isEmpty()) {
        TreeNode element = list.remove(0);
        if (element.left != null) {
            if (completeFlag) {
                return false;
            }
        list.add(element.left);
        } else {
            completeFlag = true;
        }
        if (element.right != null) {
            if (completeFlag) {
                return false;
            }
        list.add(element.right);
        } else {
            completeFlag = true;
        }
    }
        return true;
    }
}

Reference: Check the following link for a detailed explanation http://www.geeksforgeeks.org/check-if-a-given-binary-tree-is-complete-tree-or-not/