随手练——HDU Safe Or Unsafe （小根堆解决哈夫曼问题）

#include <string>
#include <map>
#include <iostream>
using namespace std;

void heapify(int *a,int index ,int length) {    
    while (index * 2 + 1 < length) {
        int left = index * 2 + 1;
        if (left + 1 < length&&a[left + 1] < a[left])left++;
        if (a[index] < a[left])break;
        swap(a[index], a[left]);
        index = left;

    }
}

void heapinsert(int *a,int index) {
    while (a[index] < a[(index - 1) / 2]) {
        swap(a[index], a[(index - 1) / 2]);
        index = (index - 1) / 2;
    }
}

int main() {
    int N;
    map<char, int>m;
    cin >> N;
    while (N--) {
        string str;
        int safe, res = 0;
        cin >> safe;
        cin >> str;
        for (int i = 0; i < str.length(); i++) {
            if (!m[str[i]]) m[str[i]] = 1;
            else m[str[i]]++;
        }
        int *a=new int[m.size()];
        int length = 0;
        for (map<char, int>::iterator it = m.begin(); it != m.end(); it++) {
            a[length++] = it->second;
        }
        for (int i = length / 2 - 1; i >= 0; i--) {
            heapify(a,i,length);
        }
        while (length > 0) {
            int m1 = a[0];
            swap(a[0], a[length - 1]);
            heapify(a, 0, --length);
            int m2 = a[0];
            swap(a[0], a[length - 1]);
            heapify(a, 0, --length);
            res += m1 + m2;
            if (length == 0)break;
            a[length] = m1 + m2;
            heapinsert(a,length++);
        }
        if (res <= safe) {
            cout << "yes" << endl;
        }
        else {
            cout << "no" << endl;
        }
        m.clear();
    }
}