Contains Duplicate II LeetCode solution in C++

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class Solution {
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 public:
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  bool containsNearbyDuplicate(vector<int> &nums, int k) {
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    unordered_map<int, int> m;
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    for (int i = 0; i < nums.size(); i++) {
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      if (m.count(nums[i]) && i - m[nums[i]] <= k) return true;
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      m[nums[i]] = i;
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    }
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    return false;
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  }
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};