• 0669. Trim a Binary Search Tree (M)


    Trim a Binary Search Tree (M)

    题目

    Given the root of a binary search tree and the lowest and highest boundaries as low and high, trim the tree so that all its elements lies in [low, high]. Trimming the tree should not change the relative structure of the elements that will remain in the tree (i.e., any node's descendant should remain a descendant). It can be proven that there is a unique answer.

    Return the root of the trimmed binary search tree. Note that the root may change depending on the given bounds.

    Example 1:

    Input: root = [1,0,2], low = 1, high = 2
    Output: [1,null,2]
    

    Example 2:

    Input: root = [3,0,4,null,2,null,null,1], low = 1, high = 3
    Output: [3,2,null,1]
    

    Example 3:

    Input: root = [1], low = 1, high = 2
    Output: [1]
    

    Example 4:

    Input: root = [1,null,2], low = 1, high = 3
    Output: [1,null,2]
    

    Example 5:

    Input: root = [1,null,2], low = 2, high = 4
    Output: [2]
    

    Constraints:

    • The number of nodes in the tree in the range [1, 10^4].
    • 0 <= Node.val <= 10^4
    • The value of each node in the tree is unique.
    • root is guaranteed to be a valid binary search tree.
    • 0 <= low <= high <= 10^4

    题意

    将BST中所有值不在指定范围内的结点删去,同时不改变BST的基本结构。

    思路

    递归处理:如果当前结点值小于左端点,则删去当前结点和左子树,递归处理右子树;如果当前结点值大于右端点,则删去当前结点和右子树,递归处理左子树;否则保留当前结点,递归处理左右子树。


    代码实现

    Java

    class Solution {
        public TreeNode trimBST(TreeNode root, int low, int high) {
            if (root == null) {
                return null;
            }
    
            if (root.val > high) {
                return trimBST(root.left, low, high);
            } else if (root.val < low){
                return trimBST(root.right, low, high);
            } else {
                root.left = trimBST(root.left, low, high);
                root.right = trimBST((root.right), low, high);
                return root;
            }
        }
    }
    
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  • 原文地址:https://www.cnblogs.com/mapoos/p/14363160.html
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