530.cpp

// inOrderTraversal.cpp
/**
 * 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 {
  int min;
  int lastValue;

public:
  int getMinimumDifference(TreeNode *root) {
    min = INT_MAX;
    lastValue = -1;
    getMinimum(root);
    return min;
  }
  void getMinimum(TreeNode *root) {
    if (root->left != NULL)
      getMinimum(root->left);
    if (lastValue >= 0 && abs(lastValue - root->val) < min)
      min = abs(lastValue - root->val);
    lastValue = root->val;
    if (root->right != NULL)
      getMinimum(root->right);
  }
};