LeetCode in Kotlin
470. Implement Rand10() Using Rand7()
Medium
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 <= 105
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
import java.util.Random
/*
* The rand7() API is already defined in the parent class SolBase.
* fun rand7(): Int {}
* @return a random integer in the range 1 to 7
*/
@Suppress("kotlin:S2245")
class Solution {
private val random: Random = Random()
fun rand10(): Int {
var r1: Int
do {
var r2: Int
do { r2 = rand7() } while (r2 == 7)
if (r2 in 1..3) { r1 = rand7() } else { r1 = 7 + rand7() }
} while (r1 > 10)
return r1
}
private fun rand7(): Int {
return random.nextInt(7) + 1
}
}