check overlapping

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

bool MyCompare(pair<int,int> p1,pair<int,int> p2){return p1.first<p2.first;}
bool MyCompare2(int p1,pair<int,int> p2){return p1<p2.first;}

int NumOfIntersection(vector<int> A)
{
int N=A.size();
vector<pair<int,int>> P;
for(int i=0;i<N;i++)
{
int start_pt=i-A[i],end_pt=i+A[i];
P.push_back(pair<int,int>::pair(start_pt,end_pt));
}
sort(P.begin(),P.end(),MyCompare);
int res=0;
for(int i=0;i<N;i++)
{
vector<pair<int,int>>::iterator iter=upper_bound(P.begin()+i,P.end(),P[i].second,MyCompare2);
iter--;
int id=iter-P.begin();
res+=(id-i);
}
return res;
}