class Solution {
public:
bool containsNearbyDuplicate(std::vector<int>& nums, int k) {
const int n = nums.size();
for (int i = 0; i < n; ++i) {
// check from i+1 up to i+k (but not beyond n)
for (int j = i + 1; j <= i + k && j < n; ++j) {
if (nums[i] == nums[j]) {
return true;
}
}
}
return false;
}
};