二叉树的前序、中序、后序遍历(c++)

• binaryTree.h

#pragma once
#include <iostream>
#include <vector>
#include <queue>
using namespace std;

struct TreeNode{
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x),left(NULL),right(NULL) {}
};

TreeNode* initBTree(int elements[], int size);

void preOrder(TreeNode* root, vector<int> &result);

void inOrder(TreeNode* root, vector<int> &result);

void postOrder(TreeNode* root, vector<int> &result);

void traverse(vector<int> nums);

• binaryTree.cpp

#include "binaryTree.h"

TreeNode* initBTree(int elements[], int size){
    if(size < 1){
        return NULL;
    }
    // nodes指针指向存放二叉树节点的数组
    // elements[] = {1,2,3,4,0,5,6,0,7};
    TreeNode **nodes = new TreeNode*[size];
    for(int i = 0; i < size; i++){
        if(elements[i] == 0){
            nodes[i] = NULL;
        }else{
            nodes[i] = new TreeNode(elements[i]);
        }
    }
    queue<TreeNode*> nodeQueue;
    nodeQueue.push(nodes[0]);
    TreeNode *node;
    int index = 1;
    while(index < size){
        node = nodeQueue.front();
        nodeQueue.pop();
        nodeQueue.push(nodes[index++]);
        node->left = nodeQueue.back();
        nodeQueue.push(nodes[index++]);
        node->right = nodeQueue.back();
    }
    return *nodes;
}

void preOrder(TreeNode* root, vector<int> &result){
    if(root){
        result.push_back(root->val);
        preOrder(root->left,result);
        preOrder(root->right,result);
    }
}

void inOrder(TreeNode* root, vector<int> &result){
    if(root){
        inOrder(root->left, result);
        result.push_back(root->val);
        inOrder(root->right,result);
    }
}

void postOrder(TreeNode* root, vector<int> &result){
    if(root){
        postOrder(root->left, result);
        postOrder(root->right,result);
        result.push_back(root->val);
    }
}

void traverse(vector<int> nums){
    int length = nums.size();
    for(int i = 0; i < length; i++){
        cout<<nums[i]<<' ';
    }
    cout<<endl;
}

int main(){
    int nums[] = {1,2,3,4,0,5,6,0,7};
    TreeNode *root = initBTree(nums, 9);
    vector<int> preResult;
    vector<int> inResult;
    vector<int> postResult;
    preOrder(root, preResult);
    inOrder(root, inResult);
    postOrder(root, postResult);
    cout<<"前序遍历的结果：" <<'\n';
    traverse(preResult);
    cout<<"中序遍历的结果：" <<'\n';
    traverse(inResult);
    cout<<"后序遍历的结果：" <<'\n';
    traverse(postResult);
    return 0;
}```