530-二叉搜索树的最小绝对差

/**
 * 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) {
        vector<int>arr;
        inorder(root, arr);
        int minNum = arr[1] - arr[0];
        for (int i = 2; i < arr.size(); i++) {
            if (arr[i] - arr[i - 1] < minNum) {
                minNum = arr[i] - arr[i - 1];
            }
        }
        return minNum;
    }
    void inorder(TreeNode *root, vector<int>&arr) {
        if (root == NULL) {
            return;
        }
        inorder(root->left, arr);
        arr.push_back(root->val);
        inorder(root->right, arr);
    }
};