这里主要是三种遍历，先序（preorder，NLR），中序（Inorder，LNR），后序（Postorder，LRN）
N：node，L：left，R：right
基本排序：先序（NLR，节点，左，右），中序（LNR，左，节点，右），后序（LRN，左，右，节点）
要点：在每一种排序里，必须遵守基本排序。看图：
为了更加直观的了解，看下面的c语言实现的代码，参考了：https://www.geeksforgeeks.org/tree-traversals-inorder-preorder-and-postorder/
#include<cstdio> #include<cstdlib> using namespace std; struct node{ int data; struct node* left; struct node* right; }; struct node* newNode(int data){ struct node* node = (struct node*)malloc(sizeof(struct node)); node->data=data; node->left=NULL; node->right=NULL; return node; } void printPostorder(struct node* node){ if(node == NULL) return; printPostorder(node->left); printPostorder(node->right); printf("%d ",node->data); } void printInorder(struct node* node){ if(node==NULL){ return; } printInorder(node->left); printf("%d ",node->data); printInorder(node->right); } void printPreorder(struct node* node){ if(node==NULL){ return; } printf("%d ",node->data); printPreorder(node->left); printPreorder(node->right); } int main(){ struct node *root=newNode(1); root->left=newNode(2); root->right=newNode(3); root->left->left=newNode(4); root->left->right=newNode(5); root->right->left=newNode(6); root->right->right=newNode(7); root->left->left->left=newNode(8); root->left->left->right=newNode(9); root->left->right->left=newNode(10); root->left->right->right=newNode(11); root->right->left->left=newNode(12); root->right->left->right=newNode(13); root->right->right->left=newNode(14); root->right->right->right=newNode(15); printf(" Preorder raversal of binary tree is "); printPreorder(root); printf(" Inorder raversal of binary tree is "); printInorder(root); printf(" Postorder raversal of binary tree is "); printPostorder(root); return 0; }
输出：
Preorder raversal of binary tree is 1 2 4 8 9 5 10 11 3 6 12 13 7 14 15 Inorder raversal of binary tree is 8 4 9 2 10 5 11 1 12 6 13 3 14 7 15 Postorder raversal of binary tree is 8 9 4 10 11 5 2 12 13 6 14 15 7 3 1
写一个中序输出的图解：
