Question

你好，我建议我学会非递归地写东西，以便更清楚地了解程序中的内容。它是一个二进制搜索程序，它读取总统列表的.dat文件并按字母顺序对它们进行排序。这是我想要非递归的代码：

BstNode* Insert(BstNode* root, string data) {

if (root == NULL) {
    root = GetNewNode(data);
}
else if (data <= root->data) {
    root->left = Insert(root->left, data);
}
else {
    root->right = Insert(root->right, data);
}
return root;

}

我想了解递归是什么以及如何查看递归的内容并使其不递归。我无法理解这些概念。如果我将该部分设置为非递归的话，我不确定是否需要调整二进制搜索树的其余部分。

这是完整的程序，以防您需要查看其他内容：

       #include <stdio.h>
       #include <iostream>
       #include <fstream>
       #include <string>
       using namespace std;

struct BstNode {

    string data;
    BstNode* left;
    BstNode* right;

};

BstNode* GetNewNode(string data) {

    BstNode* newNode = new BstNode();
    newNode->data = data;
    newNode->left = newNode->right = NULL;
    return newNode;

}



BstNode* Insert(BstNode* root, string data) {

    if (root == NULL) {
        root = GetNewNode(data);
    }
    else if (data <= root->data) {
        root->left = Insert(root->left, data);
    }
    else {
        root->right = Insert(root->right, data);
    }
    return root;

}

bool Search(BstNode* root, string data) {

    if (root == NULL) return false;
    else if (root->data == data) return true;
    else if (data <= root->data) return Search(root->left, data);
    else return Search(root->right, data);

}

void Print(BstNode*x) {

    if (!x) return;
    Print(x->left);
    cout << ' ' << x->data << endl;
    Print(x->right);
}

int main() {

    BstNode* root = NULL; //creating an empty tree
    //root = Insert(root, "adam");  test
    //root = Insert(root, "greg");  test
    //root = Insert(root, "tom");   test
    //root = Insert(root, "bill");  test
    //root = Insert(root, "sarah"); test
    //root = Insert(root, "john");  test

    ifstream fin;
    fin.open("prez.dat");
    string currentprez;
    string input = "";

    while (!fin.eof()) {

        fin >> currentprez;
        root = Insert(root, currentprez);
    }

    for (;;) {
            string input = "";
            cout << "Would you like to 'search', 'insert', 'print' or 'quit'?\n";
            cin >> input;

            //if user searches
            if (input == "search" || input == "Search") {

                string searchstr = "";
                cout << "Enter string to be searched: \n";
                cin >> searchstr;
                if (Search(root, searchstr) == true) cout << searchstr + " was Found\n";
                else cout << "Not Found\n";

            } 
            //if user inserts
            else if (input == "insert" || input == "Insert") {

                string insertstr = "";
                cout << "Enter string to be inputted: \n";
                cin >> insertstr;
                if (Search(root, insertstr) == true) cout << insertstr + " already exists\n";
                else root = Insert(root, insertstr);

            }

            //if user prints
            else if (input == "print" || input == "Print") Print(root);
            //if user quits
            else if (input == "quit" || input == "Quit") return(0);
            //if anything else
            else cout << "Invalid input\n";


        }


    }

Answer 1

像这样的树算法实际上非常适合递归，但是没有递归的方法就可以这样：

BstNode* Insert(BstNode* root, string data) {
    if (root == null) {
        return GetNewNode(data);
    }    

    BstNode* prev = null;
    BstNode* pos = root;
    while (pos != null) {
        prev = pos;
        if (data <= pos->data) {
            pos = pos->left;
        }
        else {
            pos = pos->right;
        }
   }
   if ( data <= prev -> data) {
       prev -> left = GetNewNode(data);
   }else {
       prev -> right = GetNewNode(data);
   }

   return root;
}

如何使这个函数非递归？

1 个答案: