天池 在线编程 回合制游戏（前缀和）

n, atk[i] <= 100000
答案可能超过 int 范围

示例
样例 1：
输入：atk = [19,3]
输出：3

样例 2：
输入：atk = [1,3,2,5]
输出：10

class Solution {
public:
    /**
     * @param atk: the atk of monsters
     * @return: Output the minimal damage QW will suffer
     */
    long long getAns(vector<int> &atk) {
        // Write your code here
        sort(atk.rbegin(), atk.rend());
        int n = atk.size();
        vector<long long> tailsum(n+1, 0);
        for(int i = n-1; i >= 0; --i)
            tailsum[i] = tailsum[i+1]+atk[i];
        long long life = 0;
        for(int i = 1; i < n; ++i)
            life += tailsum[i];//后序活着的怪兽 攻击的生命值之和
        return life;
    }
};

class Solution {
public:
    /**
     * @param atk: the atk of monsters
     * @return: Output the minimal damage QW will suffer
     */
    long long getAns(vector<int> &atk) {
        // Write your code here
        sort(atk.rbegin(), atk.rend());
        int n = atk.size();
        long long life = 0;
        for(int i = 1; i < n; ++i)
            life += 1LL*i*atk[i];
        return life;
    }
};