All Possible Full Binary Trees
给一个数字n, 求n个nodes组成的二叉树.
这里注意几个corn cases, 比如0,1,2
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 |
/** * 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; * } * } */ class Solution { List<TreeNode>[] lists = new List[21]; public List<TreeNode> allPossibleFBT(int n) { List<TreeNode> res = new LinkedList(); if(n <= 0) return res; if(n == 1){ res.add(new TreeNode(0)); return res; } if(n % 2 != 1){ return res; } if(lists[n] != null){ return lists[n]; } for(int i = 0; i < n; i++) { int j = n - i - 1; for (TreeNode left: allPossibleFBT(i)) for (TreeNode right: allPossibleFBT(j)) { TreeNode node = new TreeNode(0); node.left = left; node.right = right; res.add(node); } } lists[n] = res; return res; } } |