统计一串字符中每个字符的出现次数，以及哈夫曼树的WPL

WPL：weight path length  树的带权路径长度 

#include 
using namespace std;

int main() {
    int arr[30];
    memset(arr, 0, sizeof(arr));
    string s;
    cin >> s;
    for (int i = 0; i < s.length(); i++) {
        arr[s[i] - 'A']++;
    }
    priority_queue, greater > que;//优先队列greater是小的做top，>>连着会当做右移运算符
    for (int i = 0; i < 30; i++) {
        if(arr[i] > 0) {
            que.push(arr[i]);
        }
    }
    int sum = 0;
    int ans = 0;
    int flag = 1;
    if (que.size() == 1) {
        ans = que.top();
        flag = 0;
    }
    while (que.size() > 1 && flag) {
        int t1 = que.top();
        que.pop();
        int t2 = que.top();
        que.pop();
        sum = t1 + t2;
        ans += sum;
        que.push(sum);
    }
    cout << "WPL是" << ans << endl;
    return 0;
}