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GenerateTreesBst95.java
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GenerateTreesBst95.java
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package Leetcode;
import java.util.LinkedList;
import java.util.List;
public class GenerateTreesBst95 {
/**Method: Recursive; Time:O(nG(n)); Space: O(nG(n)), G(n) is Catalan number **/
public List<TreeNode> generateTrees(int n) {
if(n == 0) {
return new LinkedList<>();
}
return createTrees(1, n);
}
private List<TreeNode> createTrees(int start, int end) {
List<TreeNode> trees = new LinkedList<>();
if(start > end) {
trees.add(null);
return trees;
}
for(int i = start; i<= end; i++) {
List<TreeNode> leftTrees = createTrees(start, i-1);
List<TreeNode> rightTrees = createTrees(i+1, end);
for(TreeNode left: leftTrees) {
for(TreeNode right: rightTrees) {
TreeNode node = new TreeNode(i);
node.left = left;
node.right = right;
trees.add(node);
}
}
}
return trees;
}
//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;
}
}
}