3Sum LeetCode solution in C++

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class Solution {
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 public:
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  vector<vector<int>> threeSum(vector<int> &nums) {
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    sort(nums.begin(), nums.end());
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    vector<vector<int>> ans;
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    for (int i = 0; i < nums.size() - 2; i++) {
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      if (i > 0 && (nums[i] == nums[i - 1])) continue;
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      int left_index = i + 1;
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      int right_index = nums.size() - 1;
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      while (left_index < right_index) {
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        int threesome = nums[i] + nums[left_index] + nums[right_index];
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        if (threesome > 0)
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          right_index--;
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        else if (threesome < 0)
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          left_index++;
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        else {
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          ans.push_back({nums[i], nums[left_index], nums[right_index]});
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          while (((left_index < right_index) && nums[left_index] == nums[left_index + 1]))
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            left_index++;
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          left_index++;
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        }
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      }
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    }
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    return ans;
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  }
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};