奶牛狂欢节加强版(MooFest G) 题解

思路分析

按题目要求使用对应数据结构与算法模拟/递推求解，注意数据范围边界与时间复杂度。

参考代码

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

const int MAX_X = 50005;

struct BIT {
    long long tree[MAX_X];
    void add(int idx, long long v) {
        for (int i = idx; i < MAX_X; i += i & -i) tree[i] += v;
    }
    long long query(int idx) const {
        long long s = 0;
        for (int i = idx; i > 0; i -= i & -i) s += tree[i];
        return s;
    }
} bitCnt, bitSum;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    if (!(cin >> n)) return 0;
    vector<pair<long long, int>> cows(n);
    for (int i = 0; i < n; ++i) {
        cin >> cows[i].first >> cows[i].second;
    }
    sort(cows.begin(), cows.end());
    const long long MOD = 998244353LL;
    long long totalX = 0;
    long long ans = 0;
    for (int i = 0; i < n; ++i) {
        long long v = cows[i].first;
        int x = cows[i].second;
        long long cntL = bitCnt.query(x);
        long long sumL = bitSum.query(x);
        long long cntR = i - cntL;
        long long sumR = totalX - sumL;
        long long distSum = (cntL * x - sumL) + (sumR - cntR * x);
        ans = (ans + (distSum % MOD) * (v % MOD)) % MOD;
        bitCnt.add(x, 1);
        bitSum.add(x, x);
        totalX += x;
    }
    cout << ans << "\n";
    return 0;
}