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LeetCode Unique Binary Search Trees II
Given n, generate all structurally unique BST‘s (binary search trees) that store values 1...n.
For example,
Given n = 3, your program should return all 5 unique BST‘s shown below.
1 3 3 2 1 \ / / / \ 3 2 1 1 3 2 / / \ 2 1 2 3
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; left = null; right = null; } 8 * } 9 */10 public class Solution {11 public List<TreeNode> generateTrees(int n) {12 return create(1, n);13 }14 15 List<TreeNode> create(int start,int end) {16 List<TreeNode> results = new ArrayList<TreeNode>();17 if (start > end) {18 results.add(null);19 return results;20 }21 22 for (int k = start; k <= end; k++) {23 List<TreeNode> left = create(start, k - 1);24 List<TreeNode> right = create(k + 1, end);25 for (int i = 0; i < left.size(); i++) {26 for (int j = 0; j < right.size(); j++) {27 TreeNode root = new TreeNode(k);28 root.left = left.get(i);29 root.right = right.get(j);30 results.add(root);31 }32 }33 }34 return results;35 }36 }
LeetCode Unique Binary Search Trees II
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