灰哥的二叉樹

//這是一個教灰哥用陣列寫二叉樹的教程
//題意：知道中序後序遍歷求先序遍歷
#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
using namespace std;
const int N=10;
int la,lb;
char a[N],b[N];
struct node{
    int ls,rs;
    char c;
}tree[N];
int cnt=0;
int build(int l,int r,int s,int t){
    if(l>r||s>t) return 0;
    tree[++cnt].c=b[t]; int u=cnt;
    int root=0;
    for(root=l;root<=r;root++) if(a[root]==b[t]) break;
    tree[u].ls=build(l,root-1,s,s+root-l-1);
    tree[u].rs=build(root+1,r,s+root-l,t-1); 
    return u;
}
void print(int u){
    if(u==0) return;
    printf("%c",tree[u].c);
    print(tree[u].ls);
    print(tree[u].rs);
}
int main(){
    scanf("%s%s",a+1,b+1);
    la=strlen(a+1);lb=strlen(b+1);
    build(1,la,1,lb);  
    print(1);  
}