All unique 3 pair numbers that adds equal to target sum

-
 class Solution
{
public:
    vector<vector<int>> threeSum(vector<int> &a)
    {
        vector<vector<int>> vr;
        int i, sum, j, x, k, n = a.size();
        sum = 0;
        sort(a.begin(), a.end());
        for (i = 0; i < n; i++)
        {
            if (i != 0 && a[i] == a[i - 1])
                continue;
            x = sum - a[i];
            j = i + 1;
            k = n - 1;
            while (j < k)
            {
                if (a[j] + a[k] == x)
                {
                    vr.push_back({a[i], a[j], a[k]});
                    j++;
                    k--;
                    while (a[j] == a[j - 1] && j < k)
                        j++;
                    while (a[k] == a[k + 1] && j < k)
                        k -= 1;
                }
                else if (a[j] + a[k] > x)
                {
                    k -= 1;
                    while (a[k] == a[k + 1] && j < k)
                        k -= 1;
                }
                else if (a[j] + a[k] < x)
                {
                    j += 1;
                    while (a[j] == a[j - 1] && j < k)
                        j++;
                }
            }
        }
        return vr;
    }
};

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