Today I have done leetcode's February LeetCoding Challenge with cpp.

February LeetCoding Challenge 9

Description

Count Number of Bad Pairs

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 long countBadPairs(vector<int>& nums) {
    map<long long, long long> offsets;
    long long answer = 0;
    for(int i = 0; i < nums.size(); ++i) {
      long long offset = nums[i] - i;
      answer += i - offsets[offset];
      offsets[offset] += 1;
    } 
    return answer;
  }
};

// Accepted
// 65/65 cases passed (141 ms)
// Your runtime beats 7.29 % of cpp submissions
// Your memory usage beats 39.21 % of cpp submissions (89.3 MB)