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783. 二叉搜索树节点最小距离

/*** 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 minDiffInBST(TreeNode* root) {int ans = INT_MAX, pre = -1;dfs(root, pre, ans);return ans;}void dfs(TreeNode* root, int& pre, int& ans){//递归返回条件if(root == nullptr){return;}//前-一直递归到左下角dfs(root->left, pre, ans);//中-处理数据，第一次pre保存左下角值if(pre == -1){pre = root->val;}else{//递归退回到左下角父节点，ans取最小ans = min(ans, root->val - pre);//pre更新到当前节点的valpre = root->val;}//后续dfs(root->right, pre, ans);}
};