C :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define swap(A,B,C) (C)=(A),(A)=(B),(B)=(C)
typedef struct{
char value;
int weight;
int parent;
int lchild;
int rchild;
}HTNode, *HuffmanTree;

typedef struct{
int weight;
char value;
}pair;

void Select(HTNode HT[], int n , int *s1, int *s2){
int min1=10000, min2=10000;
for(int i = 1;i <= n; i++){
    if(HT[i].weight<min1&&HT[i].parent==0){
        min1=HT[i].weight;
        *s1=i;
    }
}
HT[*s1].parent=1;
for(int i = 1;i <= n; i++){
    if(HT[i].weight<min2&&HT[i].parent==0){
        min2=HT[i].weight;
        *s2=i;
    }
}
HT[*s2].parent=1;
if(HT[*s1].weight==HT[*s2].weight && HT[*s1].value>HT[*s2].value){
    int temp;
    swap(*s1,*s2,temp);
}
}

void HuffmanCoding(pair *w, int n){
if(n<=1) return;
int m=2*n-1;
HTNode HT[m+1];
HuffmanTree p;
int i;
for(i=1,p=&HT[i];i<=n;i++,p++,w++){
    p->weight=w->weight;
    p->value=w->value;
    p->lchild=0;
    p->rchild=0;
    p->parent=0;
}
for(;i<=m;i++,p++){
    p->lchild=0;
    p->parent=0;
    p->rchild=0;
    p->weight=0;
}
int s1=0, s2=0;
for(i=n+1;i<=m;i++){
    Select(HT,i-1,&s1,&s2);
    HT[s1].parent=i;
    HT[s2].parent=i;
    HT[i].lchild=s1;
    HT[i].rchild=s2;
    HT[i].weight=HT[s1].weight+HT[s2].weight;
    HT[i].value=HT[s1].value;
}
char HC[n+1][n];
for(i = 1;i<=n;i++){
    char cd[n];
    cd[n-1]='\0';
    int start=n-1,c,f;
    for(c=i,f=HT[i].parent;f!=0;c=f,f=HT[f].parent){
        if(HT[f].lchild==c){
            cd[--start]='0';
        }
        else{
            cd[--start]='1';
        }
    }
    strcpy(HC[i],&cd[start]);
}
for(int j=1;j<=n;j++){
    printf("%c:%s\n",HT[j].value,HC[j]);
}
}
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF){
        getchar();
    pair a[n];
    for(int i = 0;i < n; i++){
        scanf("%c",&a[i].value);
        getchar();
        scanf("%d",&a[i].weight);
        getchar();
    }

    pair *w=&a[0];
    HuffmanCoding(w,n);
    }
    return 0;
}

C++ :

#include<cstdio>
#include<queue>
#include<cstring>
#include<algorithm>
using namespace std;

int N;
char str[101];
struct Node
{
	int father, left, right, num;
	char ch, code[101];
	///结构体优先队列。对每个字符的权值排序
	///先出权值比较小的，如果权值相等，出字符较小的
	friend bool operator<(Node a, Node b)
	{
		if (a.father>b.father)
			return true;
		if (a.father == b.father&&a.ch>b.ch)
			return true;
		return false;
	}
} tree[200];
bool cmp(Node a, Node b)
{
	return a.num<b.num;
}
void dfs(int t, int i)
{///t表示huffman树的节点个数
	if (t<N)///说明t编号的节点就是叶子节点
	{
		str[i] = '\0';///str[q]='\0'，表示字符的结尾，便于后面的strcpy（）函数
		strcpy(tree[t].code, str);
		return;
	}
	else
	{
		///递归访问左孩子
		str[i] = '0';
		i++;
		dfs(tree[t].left, i);
		i--;

		///递归访问右孩子
		str[i] = '1';
		i++;
		dfs(tree[t].right, i);
		i--;

	}
}
int main()
{
	priority_queue<Node>Q;
	int n;
	while (~scanf("%d", &n))
	{
		if (n == 0)
			continue;
		memset(str, 0, sizeof(str));
		memset(tree, 0, sizeof(tree));
		for (int i = 0; i<n; i++)
		{
			getchar();
			Node node;
			scanf("%c %d", &node.ch, &node.father);
			node.num = i;///叶子节点的编号
			Q.push(node);
		}
		N = n;
		int t = 0;
		///创建huffman树
		///利用优先队列 每次选择权值最小的两个，然后将其结果在加入优先队列
		/// 将权值最小的两个  ，添加到树中
		while (Q.size()>1)
		{
			Node node1, node2, node3;
			node1 = Q.top();
			Q.pop();
			node2 = Q.top();
			Q.pop();
			node3.father = node1.father + node2.father;
			node3.ch = node1.ch;
			node3.left = node1.num;
			node3.right = node2.num;
			node3.num = n++;
			tree[t++] = node1;
			tree[t++] = node2;
			Q.push(node3);
		}
		tree[t++] = Q.top();///优先队列里面剩下一个元素，它就是根节点，直接加到树中
		Q.pop();
		sort(tree, tree + t, cmp);///按照num序号排序,最后可以按编号输出，排除非叶子节点
		dfs(t - 1, 0);
		for (int i = 0; i<N; i++)
			printf("%c:%s\n", tree[i].ch, tree[i].code);
	}
}