173. 二叉搜索树迭代器

173. 二叉搜索树迭代器

实现一个二叉搜索树迭代器。你将使用二叉搜索树的根节点初始化迭代器。

调用 next() 将返回二叉搜索树中的下一个最小的数。

示例：

BSTIterator iterator = new BSTIterator(root);

iterator.next();    // 返回 3

iterator.next();    // 返回 7

iterator.hasNext(); // 返回 true

iterator.next();    // 返回 9

iterator.hasNext(); // 返回 true

iterator.next();    // 返回 15

iterator.hasNext(); // 返回 true

iterator.next();    // 返回 20

iterator.hasNext(); // 返回 false

 

class BSTIterator {
private:
    vector<TreeNode*> S;
public:
    BSTIterator(TreeNode* root){
        while(root){
            S.push_back(root);
            root = root->left;
        }
    }
    int next() {
        TreeNode* t = S.back();
        S.pop_back();
        int val = t->val;
        t = t->right;
        while(t){
            S.push_back(t);
            t = t->left;
        }
        return val;
    }
    bool hasNext() {
        return !S.empty();
    }
};

 

测试代码：

#include<iostream>
#include<queue>
#include<vector>
using namespace std;
struct TreeNode {
    char data;
    TreeNode *left;
    TreeNode *right;
};
typedef  TreeNode* BTree;

class BSTIterator {
private:
    vector<TreeNode*> S;
    TreeNode* root;
public:
    void init(){
        root=CreateBTree();
        TreeNode* troot=root;
        while(troot){
            S.push_back(troot);
            troot = troot->left;
        }
    }
    char next() {
        TreeNode* t = S.back();
        S.pop_back();
        char val = t->data;
        t = t->right;
        while(t){
            S.push_back(t);
            t = t->left;
        }
        return val;
    }
    bool hasNext() {
        return !S.empty();
    }

    BTree  CreateBTree()
    {
        BTree bt = NULL;
        char ch;
        cin>>ch;
        if (ch != '#')
        {
            bt = new TreeNode;
            bt->data = ch;
            bt->left = CreateBTree();
            bt->right = CreateBTree();
        }
        return bt;
    }
    //层序遍历
    void LevelOrder(){
        queue<TreeNode*>q;
        TreeNode *front;
        if(root==NULL)return;
        q.push(root);
        while (!q.empty())
        {
            front = q.front();
            q.pop();
            if (front->left)
            {
                q.push(front->left);
            }
            if (front->right)
            {
                q.push(front->right);
            }
            cout<<front->data;
            
        }
    }
};


int main(){
   BSTIterator iterator;
   iterator.init();
   iterator.LevelOrder();
   cout<<endl;
   cout<<iterator.next()<<endl;
   cout<<iterator.hasNext()<<endl;
   cout<<iterator.next()<<endl;
   cout<<iterator.hasNext()<<endl;
   cout<<iterator.next()<<endl;
   cout<<iterator.hasNext()<<endl;

}

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