Solution.java

package $095;

import datastruc.TreeNode;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

/**
 * @author Junlan Shuai[shuaijunlan@gmail.com].
 * @date Created on 3:07 PM 2018/07/06.
 */
public class Solution {
    public List<TreeNode> generateTrees(int n) {
        if (n == 0){
            return new ArrayList<>();
        }

        return genTrees(1, n);
    }

    public List<TreeNode> genTrees(int start, int end) {

        List<TreeNode> list = new ArrayList<>();

        if (start > end) {
            list.add(null);
            return list;
        }

        if (start == end) {
            list.add(new TreeNode(start));
            return list;
        }

        List<TreeNode> left, right;
        for (int i = start; i <= end; i++) {

            left = genTrees(start, i - 1);
            right = genTrees(i + 1, end);

            for (TreeNode lnode : left) {
                for (TreeNode rnode : right) {
                    TreeNode root = new TreeNode(i);
                    root.left = lnode;
                    root.right = rnode;
                    list.add(root);
                }
            }

        }

        return list;
    }

}