具有 n 个节点的所有可能的完整二叉树的列表

Question

这是link问题：All Possible Full Binary Trees。

Given an integer n, return a list of all possible full binary trees with n nodes. Each node of each tree in the answer must have Node.val == 0.

Each element of the answer is the root node of one possible tree. You may return the final list of trees in any order.

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

Example 1:

Input: n = 7

Output:

[[0,0,0,null,null,0,0,null,null,0,0],
 [0,0,0,null,null,0,0,0,0],
 [0,0,0,0,0,0,0],
 [0,0,0,0,0,null,null,null,null,0,0],
 [0,0,0,0,0,null,null,0,0]]

在这个问题中，我必须 return 所有可能的完整二叉树的列表，这是我的 java 解决方案代码，任何人都可以帮助我找出我的代码出错的地方，对于每个输入，我的代码都给出空列表。

class Solution {
    public List<TreeNode> allPossibleFBT(int n) {
        if (n == 1) {
            List<TreeNode> list = new ArrayList<TreeNode>();
            list.add(new TreeNode(0));
            return list;
        }
        List<TreeNode> left;
        List<TreeNode> right;
        List<TreeNode> all = new ArrayList<TreeNode>();

        for (int i = 1; i < n; i = i + 2) {
            left = allPossibleFBT(i);
            right = allPossibleFBT(n - i - 1);

            for (int k = 0; i < left.size(); k++) {
                for (TreeNode treeNode : right) {
                    TreeNode root = new TreeNode(0);
                    root.left = left.get(k);
                    root.right = treeNode;
                    all.add(root);
                }
            }
        }
        return all;
    }
}

树节点Class:

/**
 * Definition for a binary tree node.
 */
public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode() { }

    TreeNode(int val) {
        this.val = val;
    }

    TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

Answer 1

在 for(int k=0;i<left.size();k++) 中，您需要将 i 替换为 k。