unordered_map<int, pair<int,int>> NumberToIdx;
    int MinDist = INT_MAX;

    for(int i = 0 ; i < a.size(); ++i){
        
        if(NumberToIdx.find(a[i]) == NumberToIdx.end()){
            NumberToIdx[a[i]] = make_pair(i,INT_MAX);
        }
        else{
            if(NumberToIdx[a[i]].second == INT_MAX){
                NumberToIdx[a[i]].second = i;
                MinDist = min(MinDist , (NumberToIdx[a[i]].second - NumberToIdx[a[i]].first));
            }

            else{
                int d = i - NumberToIdx[a[i]].second; 
                MinDist = min(MinDist , d);
            }
        }
    }

    if(MinDist == INT_MAX)
        return -1;
    
    return MinDist;