530.md

530. 二叉搜索树的最小绝对差

递归

中序遍历是有序数组，最小绝对差也就是相邻结点的差值。

时间复杂度：O(n)。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
private:
    int ans = INT_MAX;
    int pre = -1;
public:
    int getMinimumDifference(TreeNode* root) {
        dfs(root);
        return ans;
    }

    void dfs(TreeNode *root) {
        if (!root) {
            return;
        }
        dfs(root->left);
        if (pre == -1) {
            pre = root->val;
        } else {
            ans = min(ans, abs(root->val-pre));
            pre = root->val;
        }
        dfs(root->right);
    }
};