IT公司100题-15-求二元查找树的镜像

问题描述：

输入一颗二元查找树，将该树转换为它的镜像树，即对每一个节点，互换左右子树。

 

例如输入：

  6
/    \
4     12
/ \   /   \
2  5 8   16

输出：

  6
/     \
12     4
/   \   / \
16  8 5  2

定义二元查找树的结点为：

typedef struct BSTree {
    int data;
    BSTree* left;
    BSTree* right;
} Node;

分析：

方法1：递归交换左右子树。

// 15_1.cc
#include <iostream>
using namespace std;

typedef struct BSTree {
    int data;
    BSTree* left;
    BSTree* right;
} Node;

// 创建二元查找树
void add_BSTree_node(Node* &p_current, int data) {
    if (NULL == p_current) {
        Node *node = new Node();
        node->left = NULL;
        node->right = NULL;
        node->data = data;
        p_current = node;
    } else {
        if (p_current->data > data)
            add_BSTree_node(p_current->left, data);
        else if (p_current->data < data)
            add_BSTree_node(p_current->right, data);
        else
            cout << "The data has already in the tree.";
    }
}

// 转换二叉树为镜像树
void mirror_change(Node *root) {
    if(!root)
        return;

    // 交换左右子树
    Node* t = root->left;
    root->left = root->right;
    root->right = t;

    // 左右子树分别递归
    if(root->left)
        mirror_change(root->left);
    if(root->right)
        mirror_change(root->right);
}

// 中序打印镜像树
void print_tree(Node* root) {
    if (!root)
        return;
    cout << root->data << " ";
    print_tree(root->left);
    print_tree(root->right);
}

int main() {
    Node *root = NULL;
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );

    mirror_change(root);
    print_tree(root);
    cout << endl;
}

方法2：使用栈模仿递归过程：

// 15_2.cc
#include <iostream>
#include <stack>
using namespace std;

typedef struct BSTree {
    int data;
    BSTree* left;
    BSTree* right;
} Node;

// 创建二元查找树
void add_BSTree_node(Node* &p_current, int data) {
    if (NULL == p_current) {
        Node *node = new Node();
        node->left = NULL;
        node->right = NULL;
        node->data = data;
        p_current = node;
    } else {
        if (p_current->data > data)
            add_BSTree_node(p_current->left, data);
        else if (p_current->data < data)
            add_BSTree_node(p_current->right, data);
        else
            cout << "The data has already in the tree.";
    }
}

// 转换二叉树为镜像树
void mirror_change(Node *root) {
    if(!root)
        return;

    stack<Node*> s;
    s.push(root);
    Node* p;

    while(!s.empty()) {
        p = s.top();
        s.pop();

        // 交换左右子树
        Node* t = p->left;
        p->left = p->right;
        p->right = t;

        // 左右子树分别入栈
        if(p->left)
            s.push(p->left);
        if(p->right)
            s.push(p->right);
    }
}

// 中序打印镜像树
void print_tree(Node* root) {
    if (!root)
        return;
    cout << root->data << " ";
    print_tree(root->left);
    print_tree(root->right);
}

int main() {
    Node *root = NULL;
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );
    add_BSTree_node(root, );

    mirror_change(root);
    print_tree(root);
    cout << endl;
}