Untitled

class Solution {
public:
    long long countBadPairs(vector<int>& nums) {
        unordered_map<int, int> m;
        long long tp = 0;
        long long r = 0;
        for (int i = 0; i < nums.size(); i++) {
            tp+=i;
            int x = nums[i] - i;
            r += m[x];
            m[x]++;
        }
        return tp - r;
    }
};