2364. Count Number of Bad Pairs - Explanation

class Solution:
    def countBadPairs(self, nums: List[int]) -> int:
        n, res = len(nums), 0
        for i in range(n - 1):
            for j in range(i + 1, n):
                if j - i != nums[j] - nums[i]:
                    res += 1
        return res

class Solution:
    def countBadPairs(self, nums: List[int]) -> int:
        good_pairs = 0
        total_pairs = 0
        count = defaultdict(int)

        for i in range(len(nums)):
            total_pairs += i
            good_pairs += count[nums[i] - i]
            count[nums[i] - i] += 1

        return total_pairs - good_pairs