举个find函数的例子，以免不明白

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

using namespace std;

typedef pair<int, int> PII;

const int N = 300010;

int n, m;
int a[N], s[N];

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() {
    cin >> n >> m;
    for (int i = 0; i < n; i++) {
        int x, c;
        cin >> x >> c;
        add.push_back({x, c});  //读入坐标和值

        alls.push_back(x);  //记录坐标
    }

    for (int i = 0; i < m; i++) {
        int l, r;
        cin >> l >> r;
        query.push_back({l, r});  //需要操作的坐标和值

        //把坐标也读进alls对后面的排序计算有影响
        alls.push_back(l); 
        alls.push_back(r);
    }


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


    //找到对应的值放进去，离散化
    for (auto item : add) {
        int x = find(item.first);
        a[x] += item.second;
    }

    //前缀和预处理
    for (int i = 1; i <= alls.size(); i++) 
        s[i] = s[i - 1] + a[i];


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

    return 0;

}