离散化算法总结

#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});
        
        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());
    
    // 处理插入
    for (auto item : add)
    {
        int x = find(item.first);
        a[x] += item.second;
    }
    
    // 预处理前缀和
    for (int i = 1; i <= alls.size(); i++) s[i] = s[i - 1] + a[i];
    
    // 处理询问
    for (auto item : query)
    {
        int l = find(item.first), r = find(item.second);
        cout << s[r] - s[l - 1] << endl;
    }
    
    return 0;
}

vector<int>::iterator unique(vector<int>& a)
{
    int j = 0;
    for (int i = 0; i < a.size(); i++)
        if (!i || a[i] != a[i - 1])
            a[j++] = a[i];
    // a[0] ~ a[j - 1] 所有a中不重复的数
    
    return a.begin() + j;
}