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2364. Count Number of Bad Pairs

Difficulty Topics

Description

You are given a 0-indexed integer array nums. A pair of indices (i, j) is a bad pair if i < j and j - i != nums[j] - nums[i].

Return the total number of bad pairs in nums.

 

Example 1:

Input: nums = [4,1,3,3]
Output: 5
Explanation: The pair (0, 1) is a bad pair since 1 - 0 != 1 - 4.
The pair (0, 2) is a bad pair since 2 - 0 != 3 - 4, 2 != -1.
The pair (0, 3) is a bad pair since 3 - 0 != 3 - 4, 3 != -1.
The pair (1, 2) is a bad pair since 2 - 1 != 3 - 1, 1 != 2.
The pair (2, 3) is a bad pair since 3 - 2 != 3 - 3, 1 != 0.
There are a total of 5 bad pairs, so we return 5.

Example 2:

Input: nums = [1,2,3,4,5]
Output: 0
Explanation: There are no bad pairs.

 

Constraints:

  • 1 <= nums.length <= 105
  • 1 <= nums[i] <= 109

Solution

count-number-of-bad-pairs.py
class Solution:
    def countBadPairs(self, nums: List[int]) -> int:
        n = len(nums)
        total = n * (n - 1) // 2
        good = 0

        mp = defaultdict(int)
        # j - i != nums[j] - nums[i]
        # Bad = j - nums[j] != i - nums[i]

        for i, x in enumerate(nums):
            good += mp[x - i]
            mp[x - i] += 1

        return total - good