leetcode 530. Minimum Absolute Difference in BST

Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.

Example:

Input:

1
\
3
/
2

Output:
1

Explanation:
The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).

题目大意，求bst树任意两点的最小绝对距离。

思路，中序遍历记录先前结点和当前结点的绝对距离，保存最小的。

/**
* 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 ans = 1000000;
void dfs(TreeNode* root, int& pre) {
if (root == nullptr) return ;
dfs(root->left, pre);
if (pre != -1) ans = min(root->val-pre, ans);
//cout << "pre " << pre << "    " << root->val << endl;
pre = root->val;
dfs(root->right, pre);
}
int getMinimumDifference(TreeNode* root) {
int pre = -1;
dfs(root, pre);
return ans;
}
};