int val;

TreeNode *left;

TreeNode *right;

TreeNode(int x) : val(x), left(NULL), right(NULL) {}

vector<int> travel(TreeNode* root)

{

vector<int> res;

if (root == NULL)

return res;

res = travel(root->left);

res.push_back(root->val);

vector<int> rightChildren = travel(root->right);

res.insert( res.end(), rightChildren.begin(), rightChildren.end() );

return res;

}

int getMinimumDifference(TreeNode* root) {

vector<int> nums = travel(root);

if (nums.size()<2)

return -1; // shouldn't reach here

int res=abs(nums[1]-nums[0]);

for (size_t i=1; i<nums.size(); ++i)

{

res = min(res, abs(nums[i]-nums[i-1]));

}

return res;

}

{

Solution solution;

return 0;

}