Problem
Given the API rand7() that generates a uniform random integer in the range [1, 7], write a function rand10() that generates a uniform random integer in the range [1, 10]. You can only call the API rand7(), and you shouldn't call any other API. Please do not use a language's built-in random API.
Each test case will have one internal argument n, the number of times that your implemented function rand10() will be called while testing. Note that this is not an argument passed to rand10().
Example 1:
Input: n = 1
Output: [2]
Example 2:
Input: n = 2
Output: [2,8]
Example 3:
Input: n = 3
Output: [3,8,10]
Constraints:
1 <= n <= 10^5
Follow up:
What is the expected value for the number of calls to
rand7()function?Could you minimize the number of calls to
rand7()?
Solution (Java)
public class Solution {
private final Random random = new Random();
public int rand10() {
int x = rand7();
int y = rand7();
int value = (x - 1) * 7 + y;
if (value >= 41) {
return rand10();
}
return value % 10 + 1;
}
private int rand7() {
return random.nextInt(7) + 1;
}
}
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).