题目地址：HDU 1710

已知二叉树先序和中序求后序。

#include <stdio.h>
#include <string.h>
int a[1001], cnt;
typedef struct node
{
    int date ;
    node *lchild , *rchild ;
}*tree;
int getk(int ch,int ino[],int is,int n)
{
    for(int i = is ; i <= is + n -1 ; i++)
        if(ino[i]==ch)return i;
}
void gettree(tree &t,int pre[],int ino[],int ps,int is,int n)
{
    if(n==0) t = NULL;
    else
    {
        t = new node;
        t->date = pre[ps];
        int k = getk(pre[ps],ino,is,n);
        if(k == is) t->lchild = NULL;
        else
            gettree(t->lchild,pre,ino,ps+1,is,k-is);
        if(k == is+n-1) t->rchild = NULL;
        else
            gettree(t->rchild,pre,ino,ps+1+(k-is),k+1,n-1-(k-is));
    }
}
void pritree1(tree t)
{
    if(t)
    {
        pritree1(t->lchild);
        pritree1(t->rchild);
        a[cnt++]=t->date;
    }
}
int main()
{
    int i, n, t;
    int pre[1001] , ino[1001] ;
    while(scanf("%d", &n)!=EOF)
    {
        cnt=0;
        tree head;
        for(i=0; i<n; i++)
        {
            scanf("%d",&pre[i]);
        }
        for(i=0; i<n; i++)
        {
            scanf("%d",&ino[i]);
        }
        gettree(head,pre,ino,0,0,n);
        pritree1(head);
        for(i=0; i<cnt-1; i++)
            printf("%d ",a[i]);
        printf("%d\n",a[cnt-1]);
    }
    return 0;
}