783. 二叉搜索树节点最小距离

minDiffInBST.cpp

/**
 * 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) {}
 * };
 */


void add(TreeNode* p, std::stack<TreeNode*>* s) {
    while (p != nullptr) {
        s->push(p);
        p = p->left;
    }
}

class Solution {
public:
    int minDiffInBST(TreeNode* root) {
        int res = 9999999;
        std::stack<TreeNode*> stack;
        add(root, &stack);

        int pre = -1;

        while (!stack.empty()) {
            auto* n = stack.top();
            auto cur = n->val;
            if (pre != -1) {
                res = std::min(res, cur - pre);
            }
            pre = cur;
            stack.pop();
            add(n->right, &stack);
        }
        return res;
    }
};