leetcode-530. Minimum Absolute Difference in BST

/**
* 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);
}
}
};