代码随想录：二叉搜索树的最小绝对值

遍历二叉搜索树，定义一个全局的上一个节点确实好用

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int res = 100001;
    TreeNode* pre = NULL;
    int getMinimumDifference(TreeNode* root) {
        tra(root);
        return res;
    }
    void tra(TreeNode* node){
        if(!node)return;
        tra(node->left);
        if(pre!=NULL){
            res = min(res,node->val-pre->val);
        }
        pre = node;
        tra(node->right);

    }
};