区间统计问题(Subarray Range Count) 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 <string>
#include <algorithm>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    if (!(cin >> n)) return 0;
    vector<long long> a(n), b(n);
    for (int i = 0; i < n; ++i) cin >> a[i];
    for (int i = 0; i < n; ++i) cin >> b[i];
    vector<pair<long long, long long>> stk;
    stk.reserve(n);
    long long curS = 0;
    __int128 ans = 0;
    for (int i = 0; i < n; ++i) {
        long long cnt = 1;
        while (!stk.empty() && stk.back().first <= a[i]) {
            curS -= stk.back().first * stk.back().second;
            cnt += stk.back().second;
            stk.pop_back();
        }
        stk.push_back({a[i], cnt});
        curS += a[i] * cnt;
        ans += (__int128)curS * b[i];
    }
    if (ans == 0) {
        cout << 0 << "\n";
        return 0;
    }
    bool neg = false;
    if (ans < 0) {
        neg = true;
        ans = -ans;
    }
    string out;
    while (ans > 0) {
        out.push_back(char('0' + (int)(ans % 10)));
        ans /= 10;
    }
    if (neg) out.push_back('-');
    reverse(out.begin(), out.end());
    cout << out << "\n";
    return 0;
}