离散化

有点难理解

AcWing 804.区间和

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
typedef pair<int, int> PII;

const int N = 3e5 + 10;

int a[N], s[N]; // 最终数字存储在 a[i]

vector <int> alls;
vector <PII> add, query;

int find(int x)
{
    int l = 0, r = alls.size() - 1;
    while (l < r)
    {
        int mid = l + r >> 1;
        if (alls[mid] >= x) r = mid;
        else l = mid + 1;
    }
    return r + 1;
}

int main()
{
    int n, m; cin >> n >> m;

    for (int i = 0; i < n; i++)
    {
        int x, c; cin >> x >> c;
        add.push_back({x, c});

        alls.push_back(x);
    }

    for (int i = 0; i < m; i++)
    {
        int l, r; cin >> l >> r;
        query.push_back({l, r});

        alls.push_back(l);
        alls.push_back(r);
    }

    // 去重
    sort(alls.begin(), alls.end());
    alls.erase(unique(alls.begin(), alls.end()), alls.end());

    for (auto item: add)
    {
        int x = find(item.first);
        a[x] += item.second;
    }

    for (int i = 1; i <= alls.size(); i++)
        s[i] = a[i] + s[i - 1];

    for (auto item: query)
    {
        int l = find(item.first), r = find(item.second);
        cout << s[r] - s[l - 1] << endl;
    }

    return 0;
}