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AllPossibleFullBinaryTrees.java
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AllPossibleFullBinaryTrees.java
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/*
A full binary tree is a binary tree where each node has exactly 0 or 2 children.
Return a list of all possible full binary trees with N nodes. Each element of the answer is the root node of one possible tree.
Each node of each tree in the answer must have node.val = 0.
You may return the final list of trees in any order.
Example 1:
Input: 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]]
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<TreeNode> allPossibleFBT(int N)
{
List<TreeNode> res = new ArrayList<>();
if (N == 1)
{
res.add(new TreeNode(0));
return res;
}
N--;
for (int i = 1; i < N; i += 2)
{
List<TreeNode> left = allPossibleFBT(i);
List<TreeNode> right = allPossibleFBT(N - i);
for (TreeNode l : left)
{
for (TreeNode r : right)
{
TreeNode n = new TreeNode(0);
n.left = l;
n.right = r;
res.add(n);
}
}
}
return res;
}
}