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  • leetcode@ [173] Binary Search Tree Iterator (InOrder traversal)

    https://leetcode.com/problems/binary-search-tree-iterator/

    Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.

    Calling next() will return the next smallest number in the BST.

    Note: next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.

    /**
     * Definition for binary tree
     * struct TreeNode {
     *     int val;
     *     TreeNode *left;
     *     TreeNode *right;
     *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
     * };
     */
    class BSTIterator {
    public: queue<int> Q;
    public:
        BSTIterator(TreeNode *root) {
            inOrder(root, Q);
        }
        
        void inOrder(TreeNode* root, queue<int>& Q) {
            if(root != NULL) {
                inOrder(root->left, Q);
                Q.push(root->val);
                inOrder(root->right, Q);
            }
        }
    
        /** @return whether we have a next smallest number */
        bool hasNext() {
            return !Q.empty();
        }
    
        /** @return the next smallest number */
        int next() {
            int next_min = Q.front();
            Q.pop();
            return next_min;
        }
    };
    
    /**
     * Your BSTIterator will be called like this:
     * BSTIterator i = BSTIterator(root);
     * while (i.hasNext()) cout << i.next();
     */
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  • 原文地址:https://www.cnblogs.com/fu11211129/p/5222004.html
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