codeDump/cpp/KthSmallestInBST.cpp at main · akkupy/codeDump · GitHub

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// https://leetcode.com/problems/kth-smallest-element-in-a-bst/description/

/**
 * 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 solve(TreeNode* root, int k, int &i) {
        if(root==NULL)
            return -1;

        int left= solve(root->left, k, i);

        if(left!=-1)
            return left;

        i++;
        if(i==k)
            return root->val;

        return solve(root->right, k, i);

    }
    int kthSmallest(TreeNode* root, int k) {
        int i= 0;
        return solve(root, k, i);
    }
};