C :

#include <stdio.h>
struct Node
{
struct Node *lchild;
struct Node *rchild;
char c;
}Tree[50];                                                            
int loc;
struct Node *creat()
{
	Tree[loc].lchild=Tree[loc].rchild=NULL;
	return &Tree[loc++];
}
char str1[50],str2[50];
int Height (struct Node *T)  
{    
    if(T==NULL) return 0;  
    else  
    {  
        int m = Height ( T->lchild );  
        int n = Height(T->rchild);  
        return (m > n) ? (m+1) : (n+1);   
    }  
}  
  
struct Node *build(int s1,int e1,int s2,int e2)
{
struct Node* ret=creat();
ret->c=str1[s1];
int i,x;
for(i=s2;i<=e2;i++)
{
	if(str2[i]==str1[s1]){x=i;break;}
}
if(x!=s2) ret->lchild=build(s1+1,s1+(x-s2),s2,x-1);
if(x!=e2) ret->rchild=build(s1+(x-s2)+1,e1,x+1,e2);
return ret;
}
int main()
{
int n;
while(scanf("%d %s",&n,str1)!=EOF)
{
scanf("%s",str2);
loc=0;
struct Node *T=build(0,n-1,0,n-1);
printf("%d\n",Height(T));
}
return 0;
}

C++ :

#include<stdio.h>
#include <iostream>
#include <string.h>

using namespace std;

char pre[100];
char mid[100];

struct Node
{
	char value;
	struct Node *left;
	struct Node *right;
}*root;

Node* build_tree(int p_s, int p_e, int i_s, int i_e)
{
	if (p_e < p_s) return NULL;
	int i = 0;
	Node *tmp = new Node();
	for (i = i_s; i <= i_e; i++)
	{
		if (pre[p_s] == mid[i])
			break;
	}
	tmp->value = pre[p_s];

	tmp->left = build_tree(p_s + 1, p_s + i - i_s, i_s, i - 1);
	tmp->right = build_tree(p_s + i - i_s + 1, p_e, i + 1, i_e);

	return tmp;
}

int ans;

void DFS(Node *root, int lev)
{
	if (lev > ans) ans = lev;
	if (root->left != NULL)
		DFS(root->left, lev + 1);

	if (root->right != NULL)
		DFS(root->right, lev + 1);
}



int main()
{
	int n;
	while (scanf("%d", &n) != EOF)
	{
		scanf("%s%s", pre, mid);

		root = build_tree(0, n - 1, 0, n - 1);
		ans = 0;
		DFS(root, 0);
		//printf("sda\n");

		printf("%d\n", ans + 1);
	}
	return 0;
}

Java :

import java.util.Scanner;

public class Main {

	static class Node{

		Node left;
		Node right;
		char value;
	}
	
	static Node node[];
	static int N;
	
	

	static Node build_tree(String pre,String mid,Integer num){
		
		
		Node node=new Node();

		if(num==0) return null; 
			
		node.value=pre.charAt(0);
		
		int i;
		
		for (i = 0; i < num; i++) {
			if(mid.charAt(i)==pre.charAt(0))
				break;
		}
		
		
		node.left=build_tree(pre.substring(1,i+1),mid.substring(0,i),i);
		node.right=build_tree(pre.substring(i+1,pre.length()),mid.substring(i+1,mid.length()),num-i-1);
	
	    return node;
	}
	
	
	public static int getHight(Node node){
		
		int RHight=0,LHight=0;
		int THeight;
		
	    if(node==null) 
	        THeight=0; 
         else {
     		
     		LHight=getHight(node.left);
     		RHight=getHight(node.right);
     		
     		THeight=LHight>RHight? LHight:RHight;
     	    THeight++; 
		}

    
        return THeight;

	}
	
	
	public static void main(String[] args) {
		
        Scanner cin=new Scanner(System.in);
        while(cin.hasNext()){
        	
           N=cin.nextInt();
           String pre=cin.next();
           String mid=cin.next();
        
           node=new Node[N];
        
		   Node node=build_tree(pre, mid, N);
		   System.out.println(getHight(node));
        }
		
	}

}