95.不同的二叉搜尋樹Ⅱ

題解

代碼：

/**
 * 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 {
    public List<TreeNode> generateTrees(int n) {
        if(n == 0){
            return new LinkedList<TreeNode>();
        }
        return generateTrees(1,n);
    }
    public List<TreeNode> generateTrees(int start,int end){
        List<TreeNode> allTrees = new LinkedList<TreeNode>();
        if(start > end){
            allTrees.add(null);
            return allTrees;
        }

        for(int i=start;i <= end;i++){
           List<TreeNode> leftTrees = generateTrees(start,i-1);
           List<TreeNode> rightTrees = generateTrees(i+1,end);
           for(TreeNode left : leftTrees){
               for(TreeNode right : rightTrees){
                   TreeNode currTree = new TreeNode(i);
                   currTree.left = left;
                   currTree.right = right;
                   allTrees.add(currTree);
               }
           }
        }
    return allTrees;
    }
}