题目和思路
Given a binary search tree and the lowest and highest boundaries as L and R, trim the tree so that all its elements lies in [L, R] (R >= L). You might need to change the root of the tree, so the result should return the new root of the trimmed binary search tree.
Example 1:
Input:
1
/ \
0 2
L = 1
R = 2
Output:
1
\
2
Example 2:
Input:
3
/ \
0 4
\
2
/
1
L = 1
R = 3
Output:
3
/
2
/
1
递归修剪，比L小的则继续修剪当前节点的右子树；比R大的则继续修剪当前节点的左子树；若是在范围内，则将左子树设为递归左子树的返回值，右子树设为递归右子树的返回值。
代码
package tree;
/**
* Created by liqiushi on 2018/1/31.
*/
public class TrimABinarySearchTree {
public TreeNode trimBST(TreeNode root, int L, int R) {
if(root == null){
return root;
}
if(root.val < L ){
return trimBST( root.right, L, R);
}else if(root.val > R){
return trimBST( root.left, L, R);
}
root.left = trimBST( root.left, L, R);
root.right = trimBST( root.right, L, R);
return root;
}
}
