LightOJ-1016 - Brush (II) 

 IDEA: 

We can clean each dust by placing the brush on the y-axis of that point. From that point +w will cover all the points between them inclusively. For this first sort y-axis value then find points covered by each point.

Code:

//
// Created by Dabashis Kundu Shento on 5/12/20.
//

#include <bits/stdc++.h>

using namespace std;

int main() {
    int t,l=0;
    cin>>t;
    while(t--)
    {
        l++;
        int n,w;
        cin>>n>>w;
        int a,b;
        int c,d;
        vector<int> v;
        for(int i=0;i<n;i++)
        {
            cin>>a>>b;
            v.push_back(b);
        }
        sort(v.begin(),v.end());
        int ans=1;
        c=v[0];
        for(int i=1;i<n;i++)
        {
            if(v[i]-c>w)
            {
                ans++;
                c=v[i];
            }
        }
        cout<<"Case "<<l<<": "<<ans<<endl;
    }
    return 0;
}