LeetCode题解：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

题意：给定n，求出结点取值在1->n的二叉搜索树所有表示

解决思路：思路和之前的差不多，只不过为了生成树，需要用动态规划来生成子树

代码：

““java

public class Solution {

public List generateTrees(int n) {

List[] result = new List[n + 1];

result[0] = new ArrayList();

result[0].add(null);

for(int i = 1; i <= n; i++){
result[i] = new ArrayList<TreeNode>();
for(int j = 0; j < i; j++){
for(TreeNode nodeL : result[j]){
for(TreeNode nodeR : result[i - j - 1]){
TreeNode node = new TreeNode(j + 1);
node.left = nodeL;
node.right = clone(nodeR, j + 1);
result[i].add(node);
}
}
}
}

return result
;
}

private TreeNode clone(TreeNode node, int offset){
if(node == null){
return null;
}

TreeNode temp = new TreeNode(node.val + offset);
temp.left = clone(node.left, offset);
temp.right = clone(node.right, offset);
return temp;
}

}

“`