CODEWITHSUNDEEP
c++
Alen
Alen

Reputation: 1788

How to generate random numbers summing up to 100?

I need to make four random generated numbers which sum have to be 100. Those numbers have to be in range from 1 to 100.

How can I do this?

Upvotes: 2

Views: 3207

Answers (6)

Gopesh Bharadwaj
Gopesh Bharadwaj

Reputation: 160

Already answered above, but if anyone is looking for a working example to copy and try quickly:

int main()
{
std::vector<int> v1;

int randNum1 = rand()%(97) + 1;
int randNum2 = rand()%(98-randNum1) +1;
int randNum3 = rand()%(99 - (randNum1+randNum2)) +1;
int randNum4 = 100 -(randNum1+randNum2+randNum);

v1.push_back(randNum1);
v1.push_back(randNum2);
v1.push_back(randNum3);
v1.push_back(randNum4);

int sum = 0;
for(const auto &itr : v1)
{
    cout << itr <<endl;
    sum =sum+itr;
}
cout << "sum is : " << sum <<endl;

return 0;

}

Upvotes: 0

Kamouth
Kamouth

Reputation: 134

Generate the first between 1 and 100-3, the second between 1 and 100-first-2, the third between 1and 100-(first+second)-1 and the fourth = 100-(first+second+third).

Upvotes: 2

kassak
kassak

Reputation: 4194

You can generate four random numbers, for example in range 0..100, then rescale them to have 100 as sum:

x_i' = 1 + x_i*96.0/sum

This solution does not provide uniform distribution of {x_i}.

@PeterWood found better answer for this question Random numbers that add to 100: Matlab

Upvotes: 6

john.pavan
john.pavan

Reputation: 950

Nothing in the problem description says that each number has to be in the range of 1 to 100. You could just vary the mod with each pass. Something like:

int sum = 0;
std::vector<int> randomNums();
while (sum != 100) {
    const int randomNum = std::rand() % (99 - sum);
    sum += randomNum
    randomNums.push_back(randomNum);
}

Upvotes: 0

qPCR4vir
qPCR4vir

Reputation: 3571

If integer in range [1,100] (with obviusly decay to [1,97]) is what you need: 

double x1 = random(0, 1); 
double x2 = random(0, 1); 
double x3 = random(0, 1); 
double x4 = random(0, 1); 

double sum = x1+x2+x3+x4; 

int n1 = 1 + x1*96.0/sum; 
int n2 = 1 + x2*96.0/sum; 
int n3 = 1 + x3*96.0/sum; 

int n4 = 100 - n1 - n2 -n3;

Upvotes: 3

Spook
Spook

Reputation: 25927

Generate first random number from range 1..97.

Then generate second random number from range 1..(98-first)

Then generate third random number from range 1..(99-(first+last))

Finally set the last number as 100 - (first+second+third)

Upvotes: 3

Related Questions