二叉树 已知中序 后序 求前序

题意：

给出一棵二叉树的中序和后序遍历，求它的前序遍历。

代码如下：

#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <iostream>
#include <cstdlib>
using namespace std;
struct TNode
{
    char cInfo;
    TNode * pLeft;
    TNode * pRight;
};
#define NULL 0
#define LEN sizeof(TNode)
typedef TNode * pBTNode;
void vCreatTree(string sMidOrd,string sPostOrd,pBTNode pRoot)
{
    int nLen,nPos;
    char cData;
    string sMidOrd1,sMidOrd2,sPostOrd1,sPostOrd2;
    pBTNode pLSon,pRSon;
    nLen=sPostOrd.size();
    cData=sPostOrd[nLen-1];
    pRoot->cInfo=cData;
    pRoot->pLeft=NULL;
    pRoot->pRight=NULL;
    nPos=sMidOrd.find(cData);
    if(nLen>1)
    {
        if(nPos>0)
        {
            sMidOrd1=sMidOrd.substr(0,nPos);
            sPostOrd1=sPostOrd.substr(0,nPos);
            pLSon=(struct TNode *)malloc(LEN);
            pRoot->pLeft=pLSon;
            vCreatTree(sMidOrd1,sPostOrd1,pLSon);
        }
        if(nLen-1>nPos)
        {
            sMidOrd2=sMidOrd.substr(nPos+1,nLen-nPos-1);
            sPostOrd2=sPostOrd.substr(nPos,nLen-nPos-1);
            pRSon=(struct TNode *)malloc(LEN);
            pRoot->pRight=pRSon;
            vCreatTree(sMidOrd2,sPostOrd2,pRSon);
        }
    }
}
//获得前序遍历
string sGetPreOrd(pBTNode pRoot)
{
    string sRet;
    sRet="";
    if(pRoot!=NULL)
    {
        sRet+=pRoot->cInfo;
        sRet+=sGetPreOrd(pRoot->pLeft);
        sRet+=sGetPreOrd(pRoot->pRight);
    }
    return sRet;
}
// 删除树
void vDeleteTree(pBTNode pRoot)
{
    if(pRoot->pLeft!=NULL)
    {
        vDeleteTree(pRoot->pLeft);
        free(pRoot->pLeft);
        pRoot->pLeft=NULL;
    }
    if(pRoot->pRight!=NULL)
    {
        vDeleteTree(pRoot->pRight);
        free(pRoot->pRight);
        pRoot->pRight=NULL;
    }
}
//输出
void vOutput(string sOut)
{
    cout << sOut << endl;
}
int main()
{
    string sMidOrd,sPostOrd,sPreOrd;
    pBTNode pRoot;
    while(cin >> sMidOrd >> sPostOrd)
    {
        pRoot=(struct TNode *)malloc(LEN);
        vCreatTree(sMidOrd,sPostOrd,pRoot);
        sPreOrd=sGetPreOrd(pRoot);
        vOutput(sPreOrd);
        //vDeleteTree(pRoot);
        free(pRoot);
    }
    return 0;
}
/*
DCFEAB
DFECBA
*/

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