二叉树的四种遍历方法（递归非递归）

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wx5f6a96e093b03 2022-07-02 00:20:04 博主文章分类：数据结构与算法 ©著作权

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//
// Created by Administrator on 2021/8/1.
//

#ifndef C__TEST01_NODE_HPP
#define C__TEST01_NODE_HPP
#include <stack>
#include <queue>

class Node{
public:
    int value;
    Node* left;
    Node* right;
    Node(int value):value(value){
        left = NULL;
        right = NULL;
    }
};
//随便建一个二叉树
Node* treeInit(){
    Node *head = new Node(1);
    head->left = new Node(2);
    head->right = new Node(3);
    head->left->left = new Node(4);
    head->left->right = new Node(5);
    head->right->left = new Node(6);
    head->right->right = new Node(7);
    return head;
}

//前序遍历
void preOrderByRecur(Node *head){
    if(head == NULL){
        return;
    }
    cout<<head->value<<" ";
    preOrderByRecur(head->left);
    preOrderByRecur(head->right);
}

void preOrderNoRecur(Node *head){
    if(head == NULL){
        return;
    }
    stack<Node*> s;
    s.push(head);
    while(!s.empty()){
        head = s.top();
        cout<<head->value<<" ";
        s.pop();
        if(head->right != NULL){
            s.push(head->right);
        }
        if(head->left != NULL){
            s.push(head->left);
        }
    }
}

//中序遍历
void inOrderByRecur(Node* head){
    if(head == NULL){
        return;
    }
    inOrderByRecur(head->left);
    cout<<head->value<<" ";
    inOrderByRecur(head->right);
}


void inOrderByNoRecur(Node *head){
    if(head == NULL){
        return;
    }
    stack<Node *> s1;
    while(!s1.empty() || head != NULL){
        if(head!=NULL){
            s1.push(head);
            head = head->left;
        }else{
            head = s1.top();
            cout<<head->value<<" ";
            s1.pop();
            head = head->right;
        }
    }
}
//后序遍历
void proOrderByRecur(Node *head){
    if(head == NULL){
        return;
    }
    proOrderByRecur(head->left);
    proOrderByRecur(head->right);
    cout<<head->value<<" ";
}

void proOrderByNoRecur(Node* head){
    if(head == NULL){
        return;
    }
    stack<Node*> s1;
    stack<Node*> s2;
    s1.push(head);
    while(!s1.empty()){
      head = s1.top();
      s1.pop();
      s2.push(head);
    if(head->left!=NULL){
        s1.push(head->left);
    }
      if(head->right!=NULL){
          s1.push(head->right);
      }
    }
    while(!s2.empty()){
        cout<<s2.top()->value<<" ";
        s2.pop();
    }
}
//层次遍历
void boardOrder(Node *head){
    if(head == NULL){
        return;
    }
    queue<Node*> q;
    q.push(head);
    while(!q.empty()){
        head = q.front();
        cout<<head->value<<" ";
        q.pop();
        if(head->left != NULL){
            q.push(head->left);
        }
        if(head->right != NULL){
            q.push(head->right);
        }
    }
}
#endif //C__TEST01_NODE_HPP