# https://leetcode.com/problems/count-number-of-bad-pairs

from typing import List

class Solution:
    def countBadPairs(self, nums: List[int]) -> int:
        result = 0
        counts = {}
        for i in range(len(nums)):
            zero_value = nums[i] - i
            counts[zero_value] = counts.get(zero_value, 0) + 1
            result += (i + 1) - counts[zero_value]
        return result