669. Trim a Binary Search Tree

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.

669. <wbr>Trim <wbr>a <wbr>Binary <wbr>Search <wbr>Tree
Solution 1:
class Solution {
    public TreeNode trimBST(TreeNode root, int L, int R) {
        if (root == null) {
           return null;
        }
        if (root.val < L) {
          return trimBST(root.right, L, R);
        }
        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;
    }
}
Solution 2:
class Solution {
    public TreeNode trimBST(TreeNode root, int L, int R) {
        if (root == null) {
            return root;
        }
        while (root.val < L || root.val > R) {
            if (root.val < L) {
                root = root.right;
            }
            if (root.val > R) {
                root = root.left;
            }
        }
        TreeNode dummy = root;
        // Remove the invalid nodes from left subtree.
        while (dummy != null) {
            while (dummy.left != null && dummy.left.val < L) {
                dummy.left = dummy.left.right; 
                // If the left child is smaller than L, then we just keep the right subtree of it. 
            }
            dummy = dummy.left;
        }
        dummy = root;
        // Remove the invalid nodes from right subtree
        while (dummy != null) {
            while (dummy.right != null && dummy.right.val > R) {
                dummy.right = dummy.right.left;
                // If the right child is biggrt than R, then we just keep the left subtree of it. 
            }
            dummy = dummy.right;
        }
        return root;
    }
}
posted @ 2019-03-15 16:12  MarkLeeBYR  阅读(111)  评论(0)    收藏  举报