【PTA】05-树9 Huffman Codes（30 分） 优先队列

题目链接

思路：

1.记录频率

①用数组记录要编码的字符（char ch[N];）

②建立map容器Time,用Time[字符]记录字符的使用次数

2.建立Huffman树，计算出最少花费

①用优先队列建Huffman树

②计算最少花费（用队列层序遍历Huffman树）

3.比较测试数据

①花费是否最少    ----如果不是---->输出no （编码长度*字符使用次数）

②是否没有歧义    （比较前缀，用map容器，从小到大标记，每次标记前判断子段是否已经被标记）

#include 

using namespace std;

const int N = 100;
int n;
char ch[N];
map Time;

struct node
{
    char c[N];
    int len;
}code[N];

typedef struct tree
{
    int sum;
    struct tree* left;
    struct tree* right;
    char c;
}*Tree;

struct cmp
{
    bool operator()(const Tree x, const Tree y)
    {
        return x->sum > y->sum;
    }
};

int BuildHuffman()
{
    int sum = 0;//记录花费
    priority_queue, cmp> que;

    for(int i = 1; i <= n; i++)
    {
        Tree treenode = (Tree)malloc(sizeof(struct tree));
        treenode->c = ch[i];
        treenode->left = NULL;
        treenode->right = NULL;
        treenode->sum = Time[ch[i]];
        que.push(treenode);
    }
    while(que.size() > 1)
    {
        Tree lchild = que.top();
        que.pop();
        Tree rchild = que.top();
        que.pop();
        Tree father = (Tree)malloc(sizeof(struct tree));
        father->left = lchild;
        father->right = rchild;
        father->sum = lchild->sum + rchild->sum;
        que.push(father);
    }

    Tree head = que.top();
    typedef pair P;
    queue
 q;
    q.push(P(head,0));
    while(!q.empty())//树的层序遍历
    {
        P p = q.front();
        q.pop();
        if(p.first->left)
            q.push(P(p.first->left, p.second+1));
        if(p.first->right)
            q.push(P(p.first->right, p.second+1));
        if(!p.first->left && !p.first->right)
            sum += Time[p.first->c]*p.second;
    }

    return sum;
}

int cmp1(const struct node x, const struct node y)
{
    return x.len < y.len;
}

bool Only()
{
    map mp;
    sort(code+1,code+1+n,cmp1);
    string s;
    for(int i = 1; i <= n; i++)
    {
        s.clear();
        for(int j = 0; j < code[i].len; j++)
        {
            s += code[i].c[j];
            if(mp[s])
                return 0;
        }
        mp[s] = 1;
    }
    return 1;
}

int main()
{
    scanf("%d", &n);
    for(int i = 1; i <= n; i++)
    {
        scanf(" %c", &ch[i]);//ch保存字符，便于遍历所有字符
        scanf("%d", &Time[ch[i]]);//用MAP容器记录字符使用次数（方便调用）
    }

    int Minmum = BuildHuffman();//记录最优花费

    int m;
    scanf("%d", &m);
    while(m--)
    {
        int flag = 0;
        char c;
        int SumCost = 0;
        for(int i = 1; i <= n; i++)
        {
            scanf(" %c %s", &c, code[i].c);
            code[i].len = strlen(code[i].c);
            SumCost += Time[c]*code[i].len;//算花费
        }

        if(SumCost > Minmum)
            printf("No\n");
        else if(!Only())
            printf("No\n");
        else
            printf("Yes\n");
    }

    return 0;
}