530. Minimum Absolute Difference in BST

Posted 2021-01-26 ruruozhenhao

Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.

Example:

Input:

   1
         3
    /
   2

Output:
1

Explanation:
The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).

 

Note: There are at least two nodes in this BST.

 

Approach #1: C++.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int getMinimumDifference(TreeNode* root) {
        
        if (root->left != NULL)
            getMinimumDifference(root->left);
        
        if (pre != NULL) {
            imin = min(imin, root->val - pre->val);
        }
        
        pre = root;
        
        if (root->right != NULL)
            getMinimumDifference(root->right);
        
        return imin;
    }
    
private:
    int imin = INT_MAX;
    TreeNode* pre = NULL;
};

　　

Appraoch #2: Java.

public class Solution {
    TreeSet<Integer> set = new TreeSet<>();
    int min = Integer.MAX_VALUE;

    public int getMinimumDifference(TreeNode root) {
        if (root == null) return min;

        if (!set.isEmpty()) {
            if (set.floor(root.val) != null) {
                min = Math.min(min, root.val - set.floor(root.val));
            }
            if (set.ceiling(root.val) != null) {
                min = Math.min(min, set.ceiling(root.val) - root.val);
            }
        }

        set.add(root.val);

        getMinimumDifference(root.left);
        getMinimumDifference(root.right);

        return min;
    }
}

　　

At the first time, I want to use c++ to realise above code, I can use set upper_bound to replace set.ceiling but I can‘t find the suitable method to replace the set.floor.

there are some notes about java syntax:

1. The difference between int and Integer in java.

 

Approach #3: Python.

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    
    def getMinimumDifference(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        L = []
        
        def dfs(root):
            if root.left: dfs(root.left)
            L.append(root.val)
            if root.right: dfs(root.right)
                
        dfs(root)
        
        return min(abs(a-b) for a, b in zip(L, L[1:]))

　　

There are some syntax in python:

1.zip in python.