判断是否存在相距 k 以内的相同值

bool containsNearbyDuplicate(vector<int>& nums, int k) {
    unordered_map<int, list<size_t>> numIndexListDic;
    for (size_t i = 0; i < nums.size(); ++i){
        auto loc = numIndexListDic.find(nums[i]);
        if (loc == numIndexListDic.end()){
            numIndexListDic[nums[i]] = list<size_t>{i};
        }
        else{
            auto nearbyDuplicateIt = find_if(loc->second.cbegin(), loc->second.cend(), [&](size_t index){return i - index <= k;});
            if (nearbyDuplicateIt != loc->second.cend()){
                return true;
            }
            loc->second.push_back(i);
        }
    }
    return false;
}