Stripe Interview Question for Software Engineers


Country: United States




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int NextServerNumber(int[] serversTaken){
	int max = 0;
	HashSet<int> possibles = new HashSet<int>();
	
	foreach (int currentServer in serversTaken){
		if (currentServer > max){
			//we add from max to the current
			for(int i = max + 1; i < currentServer; i++){
				//add as a possible
				possibles.Add(i);
			}
			max = currentServer;
		}
		if (possibles.Contains(currentServer))
			possibles.Remove(currentServer);
	}
	
	if(possibles.Count > 0)
		return possibles[0];
		
	return max+1;
}

- Diego August 01, 2019 | Flag Reply
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This question is asking the first missing positive integer from the list of n integers. (Total n-1 integers given and return value should be an integer missing (m) from this list. So, it is implied that 1<=m<=n.

#include<iostream>
#include<vector>
using namespace std;

  int missingInt(vector<int> v) {
	int cnt=0, tmp=v[0],n=v.size(),i=0;
	while(cnt<=n) {
			if(v[i] != i+1 && v[i]<=n) {
				tmp = v[v[i]-1];
				v[v[i]-1] = v[i];
				v[i]=tmp;
			}
			else i++;
			cnt++;
	}
	int j=0;
	for( j=0;j<n;++j)
		if(v[j]!=j+1) return j+1;
	return j+1;
}

int main() {
	vector<int> v = {4,1,5,3}; // Don't sort it. Otherwise it will be n log(n).
	int ret = missingInt(v);
	cout<<ret;
	return 0;
}

- alanturing06022014 August 03, 2019 | Flag Reply
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We traverse the array containing all positive numbers and to mark presence of an element x, we change the sign of value at index x to negative. We traverse the array again and print the first index which has positive value. In the following code, findMissingPositive() function does this part. Note that in findMissingPositive, we have subtracted 1 from the values as indexes start from 0 in C.

/* Find the smallest positive missing number  
in an array that contains all positive integers */
int findMissingPositive(int arr[], int size)  
{  
    int i;  
      
    // Mark arr[i] as visited by making arr[arr[i] - 1] negative.  
    // Note that 1 is subtracted because index start  
    // from 0 and positive numbers start from 1  
    for(i = 0; i < size; i++)  
    {  
        if(abs(arr[i]) - 1 < size && arr[ abs(arr[i]) - 1] > 0)  
        arr[ abs(arr[i]) - 1] = -arr[ abs(arr[i]) - 1];  
    }  
      
    // Return the first index value at which is positive  
    for(i = 0; i < size; i++)  
        if (arr[i] > 0)  
            // 1 is added because indexes start from 0  
            return i+1;  
      
    return size+1;  
}

- Nits August 16, 2019 | Flag Reply


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