POJ 1521 Entropy

求哈夫曼树的平均码长，用优先队列来写，先记录某个字符在字符串里出现的次数，然后放入

队列。依次取出第一小和第二小的数，将两个数相加，构成新的虚拟结点，放入队列中。

/*Accepted    196K    0MS    C++    918B    2012-08-01 17:25:00*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<queue>
using namespace std;int key[1 << 7], len;
char t[1 << 10];int huffman()
{int i, a, b, c, sum = 0;priority_queue<int, vector<int>, greater<int> > q;for(i = 65; i < 100; i ++){if(key[i] > 0)q.push(key[i]);}while(q.size() > 1){a = q.top(); q.pop();b = q.top(); q.pop();c = a + b;sum += c;q.push(c);}return sum > 0 ? sum : len; //当只有一个字符的时候
}int main()
{int i, sum;while(scanf("%s", t) != EOF){if(strcmp(t, "END") == 0) break;len = strlen(t);memset(key, 0, sizeof key);for(i = 0; i < len; i ++)key[t[i]] ++;sum = huffman();printf("%d %d %.1f\n", len * 8, sum, (double)len * 8 / sum);}return 0;
}