小弟我写的建哈夫曼的程序，帮小弟我看下错哪了呢

我写的建哈夫曼的程序，帮我看下哪里错了呢
我的程序采用STL里的vector，动态存储树的节点（结构体），建树过程中采取了堆排序的办法来寻找权值最小的两个节点，找到后建立他们的父亲节点。但是运行的时候出现了段错误。这是为什么呢？

#include <iostream>

#include <vector>

#include <algorithm>


using namespace std;


typedef struct

{

    char Alpha='0';

    int Tax=65535;

    int PointerParent=65535;

    int PointerLChild=65535;

    int PointerRChild=65535;

}TNode;


bool TNodeCmp(const TNode &Cmp1,const  TNode &Cmp2)

{

    return Cmp1.Tax>Cmp2.Tax;

}


vector<TNode> MakeHaff(vector<TNode>ToHaff,int AlphaSize)

{

    vector<TNode>::iterator HeapHead=ToHaff.begin();

    int LChild=0;

    int RChild=1;

    while(HeapHead!=ToHaff.end())

    {

        make_heap(HeapHead,ToHaff.end(),TNodeCmp);

        HeapHead++;

        make_heap(HeapHead,ToHaff.end(),TNodeCmp);

        HeapHead++;

        TNode newFather;

        newFather.Tax=ToHaff[LChild].Tax+ToHaff[RChild].Tax;

        newFather.PointerLChild=LChild;

        newFather.PointerRChild=RChild;

        ToHaff.push_back(newFather);

        ToHaff[RChild].PointerParent=AlphaSize+1;

        ToHaff[LChild].PointerParent=AlphaSize+1;

        LChild=LChild+2;

        RChild=RChild+2;

        AlphaSize=AlphaSize+1;

        vector<TNode>::iterator displayP=ToHaff.end();

        TNode DNode=*displayP;

        cout<<DNode.Tax<<" ";

    }

    return ToHaff;

}



int main()

{

    vector<TNode> Al;

    TNode a1;

    a1.Tax=2;

    TNode a2;

    a2.Tax=1;

    TNode a3;

    a3.Tax=100;

    Al.push_back(a1);

    Al.push_back(a2);

    Al.push_back(a3);

    int i=0;

    while(i<5)

    {

        cout<<Al[i].Tax<<" ";

        i++;

    }

    cout<<endl;

    Al=MakeHaff(Al,3);

    i=0;

    while(i<5)

    {

        cout<<"Result:";

        cout<<Al[i].Tax<<" ";

        i++;

    }

    cout<<endl;


    return 0;