894. All Possible Full Binary Trees

Explanation

To generate all possible full binary trees with n nodes where each node has a value of 0, we can use a recursive approach. We can iterate over all possible combinations of left and right subtrees for each node. In each recursive call, we divide the remaining nodes between the left and right subtrees. If there are no remaining nodes, we return a list containing a single node with value 0. We then combine all possible combinations of left and right subtrees to form full binary trees with n nodes.

Time complexity: O(2^n)
Space complexity: O(2^n)

View Leetcode Problem

class Solution {
    public List<TreeNode> allPossibleFBT(int n) {
        List<TreeNode> result = new ArrayList<>();
        if (n % 2 == 0) {
            return result;
        }
        if (n == 1) {
            result.add(new TreeNode(0));
            return result;
        }
        
        for (int i = 1; i < n; i += 2) {
            List<TreeNode> leftSubtrees = allPossibleFBT(i);
            List<TreeNode> rightSubtrees = allPossibleFBT(n - 1 - i);
            
            for (TreeNode left : leftSubtrees) {
                for (TreeNode right : rightSubtrees) {
                    TreeNode root = new TreeNode(0);
                    root.left = left;
                    root.right = right;
                    result.add(root);
                }
            }
        }
        
        return result;
    }
}

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