哈夫曼树的构造-C语言

#include <stdio.h>#include <stdlib.h>typedef struct{    int weight,parent,lchild,rchild;} HNode;void HuffTree(HNode Huff[],int n){    int i,j,m1,m2,x1,x2;   //m1,m2代表的是每次集合中最小的两个权重，x1,x2即为他们的下标.    for(i=0; i<2*n-1; i++)    {        Huff[i].weight=0;        Huff[i].parent=-1;        Huff[i].lchild=-1;        Huff[i].rchild=-1;    }    printf("Input 1~n value of leaf:\n");    for(i=0; i<n; i++)        scanf("%d",&Huff[i].weight);    for(i=0; i<n-1; i++)              //这里n-1不是很理解    {        m1=m2=32767;        x1=x2=0;        for(j=0; j<n+i; j++)        {            if(Huff[j].parent==-1 && Huff[j].weight<m1)            {                m2=m1;                x2=x1;                m1=Huff[j].weight;                x1=j;            }            else if(Huff[j].parent==-1 && Huff[j].weight<m2)            {                m2=Huff[j].weight;                x2=j;            }        }        Huff[x1].parent=n+i;        Huff[x2].parent=n+i;        Huff[n+i].weight=Huff[x1].weight+                            Huff[x2].weight;        Huff[n+i].lchild=x1;        Huff[n+i].rchild=x2;    }    printf("Huff weight   lchild   rchild   parent\n");    for(i=0;i<2*n-1;i++)        printf("%3d%5d%10d%10d%10d\n",i,                Huff[i].weight,Huff[i].lchild,                Huff[i].rchild,Huff[i].parent);}int main(){    HNode Huff[100]={};//空间要足够大，至少要大于2n-1    HuffTree(Huff,4);    printf("Hello world!\n");    return 0;}

书上说要进行n-1次合并才能使初始的二叉树最终合并成一棵二叉树，n-1不是很理解，希望那位大神可以解惑。