经典面试题——二叉树

#include <cstdio>
#include <iostream>
#include <queue>
using namespace std;

struct Node {
    Node *l, *r;
    int x;
    Node(int x=0, Node *l=NULL, Node *r=NULL):x(x),l(l),r(r) {}    
};

class Tree {
    public:
        Tree(Node* root) {
            this->root = root;
        }
        
        Node* getRoot() {
            return root;
        }
        
        Node* buildTree() {
            int x;
            cin >> x;
            if(x != -1) {
                Node* curRoot = new Node(x);
                curRoot->l = buildTree();
                curRoot->r = buildTree();
                return curRoot;
            } else {
                return NULL;
            }
        }
        
        void print_pre_order(Node* cur) {
            if(cur == NULL)    return;
            printf("%d ", cur->x);
            print_pre_order(cur->l);
            print_pre_order(cur->r);
        }
        
        void print_in_order(Node* cur) {
            if(cur == NULL)    return;
            print_in_order(cur->l);
            printf("%d ", cur->x);
            print_in_order(cur->r);
        }
        
        void print_post_order(Node* cur) {
            if(cur == NULL)    return;
            print_post_order(cur->l);
            print_post_order(cur->r);
            printf("%d ", cur->x);
        }
        
        void print_level_order(Node* cur) {
            if(cur==NULL)    return;
            queue<Node*> que;
            que.push(cur);
            while(!que.empty()) {
                Node* c = que.front();
                que.pop();
                printf("%d ", c->x);
                if(c->l)    que.push(c->l);
                if(c->r)    que.push(c->r);
            }
        }
        
        int getNodeNum(Node* root) {
            if(root==NULL)    return 0;
            return getNodeNum(root->l) + getNodeNum(root->r) + 1;
        }
        
        int getLeafNum(Node* root) {
            if(root==NULL)    return 0;
            if(root->l==NULL && root->r==NULL)    return 1; // 是叶子节点 
            return getLeafNum(root->l) + getLeafNum(root->r); // 非叶子节点 
        }
        
        int getHeight(Node* root) {
            if(root==NULL)    return 0;
            return max(getHeight(root->l), getHeight(root->r))+1; // 每个节点都加1，所以统计了所有节点数 
        }
        
        void turn_all_node(Node *root) {
            if(root==NULL)    return;
            if(root->l==NULL && root->r==NULL)    return; // 两个分支均为空，交换无意义 
            // 左右分支交换 
            Node* temp = root->l;
            root->l = root->r;
            root->r = temp;
            if(root->l)    turn_all_node(root->l);
            if(root->r)    turn_all_node(root->r);
        }
        
        bool isExist(Node *root, int x) {
            if(root == NULL)    return 0;
            if(root->x == x)    return 1;
            return isExist(root->l, x) || isExist(root->r, x);
        }
        // 求二叉树第K层的节点个数
        int getKnum(Node *root, int k) {
            if(root==NULL || k < 1)    return 0;
            if(k==1)    return 1;
            return getKnum(root->l, k-1)+getKnum(root->r, k-1);
        }
        // 判断两棵二叉树是否结构相同
        bool cmp(Node *a, Node *b) {
            if(a == NULL && b == NULL) return 1; 
            if(a==NULL || b==NULL)    return 0;
            return cmp(a->l, b->l) && cmp(a->r, b->r);
        }
    private:
        Node *root;
};

int main ()
{
    // 1 2 4 -1 -1 5 -1 6 -1 -1 3 7 -1 8 -1 -1 -1
    // 6 4 2 3 -1 -1 -1 -1 5 1 -1 -1 7 -1 -1
    Node* root;
    Tree tree(root);
    root = tree.buildTree();
    
    // 前、中、后序遍历 
    tree.print_pre_order(root);
    printf("\n");
    
    tree.print_in_order(root);
    printf("\n");
    
    tree.print_post_order(root);
    printf("\n");
    
    tree.print_level_order(root);
    printf("\n");
    
    //节点个数
    cout << "Node num: " << tree.getNodeNum(root) << endl;
     
    // 叶子个数 
    cout << "Leaf num: " << tree.getLeafNum(root) << endl;
    
    // 树高 
    cout << "Height: " << tree.getHeight(root) << endl;
    
    // 二叉树镜像 
    tree.turn_all_node(root);
    tree.print_level_order(root);
    printf("\n");
    
    //子树的节点查找 
//    int x;
//    while(cin >> x) {
//        printf("%s\n", tree.isExist(root, x) ? "Yes!":"No.");
//    }

    //求二叉树第K层的节点个数
//    int k;
//    while(cin >> k) {
//        printf("The %dth floor nodes num: %d\n", k, tree.getKnum(root, k));
//    }

    return 0;
}