Leetcode 783. binary search tree node minimum distance tree /easy

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1.Description

Give you a binary search tree root node root , return The minimum difference between the values of any two different nodes in the tree .

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2.Example

 Input ：root = [4,2,6,1,3]
 Output ：1

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3.Solution

Using middle order traversal , Calculate the difference between the current node and the previous node .

class Solution {
    
    int pre;
    int ans;

    public int minDiffInBST(TreeNode root) {
    
        ans = Integer.MAX_VALUE;
        pre = -1;
        dfs(root);
        return ans;
    }

    public void dfs(TreeNode root) {
    
        if (root == null) {
    
            return;
        }
        dfs(root.left);
        if (pre == -1) {
    
            pre = root.val;
        } else {
    
            ans = Math.min(ans, root.val - pre);
            pre = root.val;
        }
        dfs(root.right);
    }
}