Establish binary tree + C language code from preorder and middle order

summary

describe ：
Given a preorder （ In the following order ） And middle order to build a binary tree , For example, the sequence of precedence ：ABDCEF, Subsequent sequence ：BDAECF
Build a binary tree
recursive
The first node of the preorder traversal is the root node . In the sequence traversed by middle order , On the left side of this node is the left subtree , On the right side of this node is the right subtree .
If the left subtree is not empty , Then the second node of the preorder traversal is the root node of the left subtree , Otherwise, it is the root node of the right subtree . Repeat the above steps for the left and right subtrees , Can uniquely determine a binary tree .
（ The latter sequence should be from the back to the front ）

Code

#include <stdio.h>

struct TNode{
    
	char data;
	struct TNode* left;
	struct TNode* right;
};

TNode* piTree(char *pa, char *ia, int p1, int p2, int i1, int i2)
{
    
    int ia_mid;
    TNode *T;
    T=new TNode;
    T->data=pa[p1];
    T->left=T->right=NULL;
    if(p1>p2 || i1>i2)
    	return NULL;
    for(ia_mid=0;;ia_mid++){
    
    	if(pa[p1]==ia[ia_mid])
    		break;
	}// Find the root node in the middle order sequence  
	T->left = piTree(pa,ia,p1+1,p1+(ia_mid-i1),i1,ia_mid-1);
	T->right = piTree(pa,ia,p1+(ia_mid-i1)+1,p2,ia_mid+1,i2);
 	return T;
}

void PostTravel(TNode* T)
{
    	// Post sequence printing 
	if(T==NULL) return;
	if(T->left) PostTravel(T->left);
	if(T->right) PostTravel(T->right);
	printf("%c", T->data);
}

int main()
{
    
	char pre[100], in[100];
	int n; 					// Used to save the sequence length 
	TNode *T;				// Used to save the root of binary tree 
	printf(" Input sequence ：\n");
	scanf("%s", pre);
	printf(" Input medium sequence ：\n");
	scanf("%s", in);
	n=0; 
	while(pre[n]) n++;		// Calculate the length of the sequence  
	T= piTree(pre, in, 0, n-1, 0, n-1);
	printf(" Subsequent sequence ：\n");
	PostTravel(T);			// Print sequence  
    return 0;
}

Examples of run results ：