leetcode-530. Minimum Absolute Difference in BST

考察点：平衡二叉树性质，遍历特点；
思路：BST中序遍历是有序的；
C++ 代码：

/** * 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> q;        help(q, root);        int ret = INT_MAX;        for (int i=0; i<q.size()-1; i++) {            if (q[i+1] - q[i] < ret)                ret = q[i+1] - q[i];        }        return ret;    }    void help(vector<int>& q, TreeNode * root) {        if (root->left) {                help(q, root->left);        }        q.push_back(root->val);        if (root->right) {            help(q, root->right);        }    }};