Longest Arithmetic Subsequence LeetCode solution in C++

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class Solution {
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 public:
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  int longestArithSeqLength(vector<int> &nums) {
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    int n = size(nums);
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    int ans = 1;
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    vector<vector<int>> dp(n, vector<int>(1005, 1));
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    for (int i = 1; i < n; i++)
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      for (int j = 0; j < i; j++)
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        ans = max(ans, dp[i][nums[i] - nums[j] + 500] = 1 + dp[j][nums[i] - nums[j] + 500]);
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    return ans;
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  }
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};