POJ 2255 Tree Recovery ( 二叉樹）

題意：給出一棵二叉樹的前序周遊和中序周遊，輸出這棵樹的後序周遊。

分析：根據前序和中序周遊建樹，再後續輸出即可，重點在于建樹的過程。

//116K  0MS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 30

typedef struct node
{
    char c ;
    node *left , *right ;
}*tree;

char pre[MAX] , in[MAX] ;


int Find_Index ( char c )
{

    int index ;
    index = -1 ;
    int i ;
    for ( i = 0 ; in[i] ; i ++ )
    {
        if ( in[i] == c )
        {
            index = i ;
            break ;
        }
    }
    return index ;
}

tree BuildTree ( int l_pre , int l_in , int len )
{
    tree temp ;
    temp = NULL ;
    if (  len > 0 )
    {
        temp = ( tree ) malloc ( sizeof ( node ) ) ;
        int k ;
        k = Find_Index ( pre[l_pre] ) ;
        temp->c = pre[l_pre] ;
        temp->left = BuildTree(l_pre+1, l_in, k-l_in);
        temp->right = BuildTree(l_pre+1+k-l_in, k+1, len-(k-l_in)-1);
    }
    return temp ;
}

void Print_Tree ( tree t )
{
    if ( t )
    {
        Print_Tree ( t->left ) ;
        Print_Tree ( t->right ) ;
        putchar (t->c) ;
    }
}

int
main ( )
{
    while ( 2 == scanf ("%s%s" , pre , in ) )
    {
        tree T ;
        T = BuildTree ( 0 , 0 , strlen ( pre ) ) ;
        Print_Tree ( T ) ;
        printf ("\n") ;
        free ( T ) ;
    }
    return 0 ;
}