2448. Count Number Of Bad Pairs¶

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2448. Count Number of Bad Pairs

Medium

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¶

class Solution {
    public long countBadPairs(int[] nums) {
        int n = nums.length;
        long count = 0;
        HashMap<Integer, Integer> map = new HashMap<>();
        ArrayList<Integer> res = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            int req = i - nums[i];
            count += res.size();
            count -= map.getOrDefault(req, 0);
            res.add(req);
            map.put(req, map.getOrDefault(req, 0) + 1);
        }
        return count;
    }
}

Complexity Analysis¶

• Time Complexity: O(?)
• Space Complexity: O(?)

Approach¶

Detailed explanation of the approach will be added here