Algorithm to calculate number of intersecting discs

Question

Given an array A of N integers we draw N discs in a 2D plane, such that i-th disc has center in (0,i) and a radius

Answer 1

count = 0
for (int i = 0; i < N; i++) {
  for (int j = i+1; j < N; j++) {
    if (i + A[i] >= j - A[j]) count++;
  }
}

It is O(N^2) so pretty slow, but it works.