Leetcode/leetcode173.cpp at main · ksaini-web/Leetcode · GitHub

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/**
 * 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 BSTIterator {
public:


stack <TreeNode*> st;

    void pushleft(TreeNode* root){

        while(root != NULL){

            st.push(root);
           root= root->left;

        }
    }
    BSTIterator(TreeNode* root) {

        pushleft(root);


    }

    int next() {

       TreeNode* node =st.top();

       st.pop();
       pushleft(node->right);


       return node->val;

    }

    bool hasNext() {

        return !st.empty();

    }
};

/**
 * Your BSTIterator object will be instantiated and called as such:
 * BSTIterator* obj = new BSTIterator(root);
 * int param_1 = obj->next();
 * bool param_2 = obj->hasNext();
 */