Google Interview Question for SDE1s


Country: United States




Comment hidden because of low score. Click to expand.
1
of 1 vote

between a and b, I assume a half open interval [a, b)

question is the distribution, if it should be normal, the previous posts are probably right (needs a prove though). If we want uniform distribution things are different.

I could create a random function that creates a uniform random number in the range [0 and 2^n) by applying the given function to each bit. Then I could use this new function to create a random number in the range [0, 2^n) where n would be lg2(b-a) + 1. If the random number exceeds b-a, I try again, if not, I add it to a and return the result.

- Chris December 03, 2017 | Flag Reply
Comment hidden because of low score. Click to expand.
1
of 1 vote

#include <iostream>
#include <unordered_map>

using namespace std;

bool Rand2()
{
	return rand() % 2;
}

uint32_t RandAB(uint32_t a, uint32_t b)
{
	uint32_t max_val = b - a;

	int bits = 0;
	for (uint32_t mask = 1; mask <= max_val && mask != 0; mask <<= 1) {
		++bits;
	}

	uint32_t rnd = 0;
	do {
		rnd = 0;
		for (int i = 0; i < bits; ++i) {
			rnd <<= 1;
			rnd |= Rand2();
		}
	} while (rnd > max_val);

	return a + rnd;
}

int main()
{
	srand(time(NULL));
	unordered_map<uint32_t, int> stats;
	for (int i = 0; i < 100000000; ++i) {
		++stats[RandAB(3, 14)];
	}
	for (auto &el : stats) {
		cout << el.second << "=>" << el.first << "\n";
	}
}

- Alex December 05, 2017 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

Let's call this function rand();

int randomNumber = a-1;
for(int i = 0; i < b-a; i++){
	if rand() = 0
		randomNumber++;
}

- Shitty Programmer December 02, 2017 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

Let's assume the function that randomly returns 1 or 0 is called rand() and is defined in the same class.

public int randBetweenAandB(int a, int b){
int r = a-1;
for(int i = 0; i < b-a; i++){
	if(rand() == 1)
		r++;
}


return r;

}

- I suck at code December 02, 2017 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

random function for every bit
or
rand + 2 * rand + 4*rand + ...
you can see that rand + 2 *rand output 0 1 2 3 uniformly

- zyfo2 December 04, 2017 | Flag Reply


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