重建二叉树

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=1944

这道题是练习递归并深刻理解二叉树遍历的好题目（编程之美上也有）

 

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

typedef struct Node
{
    char    chValue;
    struct Node    *lChild;
    struct Node    *rChild;
}Node;


//重建二叉树
void Rebuild(char *pPreOrder , char *pInOrder , Node **pRoot , int nTreeLen)
{
    int  nLeftLen , nRightLen;
    char *pLeftEnd;
    Node *p;

    //边界条件检查
    if(!pPreOrder || !pInOrder || !pRoot)    return;   

    if(!(p = (Node *)malloc(sizeof(Node))))    return;
    p->chValue = *pPreOrder;    
    p->lChild = p->rChild = NULL;
    *pRoot = p;
    
    if(nTreeLen == 1)    return;

    //划分左右子数
    pLeftEnd = pInOrder;
    while(*pLeftEnd != *pPreOrder)    pLeftEnd++;
    nLeftLen = (int)(pLeftEnd - pInOrder);
    nRightLen = nTreeLen - nLeftLen - 1;

    if(nLeftLen)    Rebuild(pPreOrder + 1 , pInOrder , &(p->lChild) , nLeftLen);
    if(nRightLen)   Rebuild(pPreOrder + nLeftLen + 1, pInOrder + nLeftLen + 1 , &(p->rChild) , nRightLen);
}

//后序遍历
void PostOrder(Node *p)
{
    if(p)
    {
        PostOrder(p->lChild);
        PostOrder(p->rChild);
        printf("%c",p->chValue);
    }
}

int main(void)
{
    char PreOrder[32] , InOrder[32];
    Node *pTree;

    //输入先序和中序序列
    while(scanf("%s%s", PreOrder , InOrder) != EOF)
    {
        Rebuild(PreOrder , InOrder , &pTree , strlen(PreOrder));
        PostOrder(pTree);
        printf("\n");
    }
    return 0;
}