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  • 270. Closest Binary Search Tree Value

    题目:

    Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.

    Note:

    • Given target value is a floating point.
    • You are guaranteed to have only one unique value in the BST that is closest to the target.

    链接: http://leetcode.com/problems/closest-binary-search-tree-value/

    题解:

    求BST中跟target最近的数字。我们先设置一个min = root.val,然后用iterative的办法尝试更新min, 然后比较target与root的大小,进行二分查找。

    Time Complexity - O(logn), Space Complexity - O(1)。

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    public class Solution {
        public int closestValue(TreeNode root, double target) {
            int min = root.val;
            while(root != null) {
                min = Math.abs(target - root.val) < Math.abs(target - min) ? root.val : min;
                root = root.val < target ? root.right : root.left;
            }
            
            return min;
        }
    }

    二刷:

    这道题也是主要考察binary search。方法和一刷一样。  可以有递归和迭代。

    Java:

    迭代

    Time Complexity - O(logn), Space Complexity - O(1)。

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    public class Solution {
        public int closestValue(TreeNode root, double target) {
            int min = root.val;
            while (root != null) {
                min = Math.abs(root.val - target) < Math.abs(min -target) ? root.val : min;
                root = target < root.val ? root.left : root.right;
            }
            return min;
        }
    }

    递归:

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    public class Solution {
        public int closestValue(TreeNode root, double target) {
            TreeNode child = target < root.val ? root.left : root.right;
            if (child == null) {
                return root.val; 
            }
            int childClosest = closestValue(child, target);
            return Math.abs(root.val - target) < Math.abs(childClosest - target) ? root.val : childClosest;
        }
    }

    三刷:

    Java:

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    public class Solution {
        public int closestValue(TreeNode root, double target) {
            if (root == null) return 0;
            int min = root.val;
            while (root != null) {
                min = (Math.abs(root.val - target) < Math.abs(min - target) ? root.val : min);
                root = (root.val < target) ? root.right : root.left;
            }
            return min;
        }
    }

     

    Reference:

    https://leetcode.com/discuss/54438/4-7-lines-recursive-iterative-ruby-c-java-python 

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  • 原文地址:https://www.cnblogs.com/yrbbest/p/5025951.html
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