LeetCode in Kotlin
2438. Range Product Queries of Powers
Medium
Given a positive integer n, there exists a 0-indexed array called powers, composed of the minimum number of powers of 2 that sum to n. The array is sorted in non-decreasing order, and there is only one way to form the array.
You are also given a 0-indexed 2D integer array queries, where queries[i] = [lefti, righti]. Each queries[i] represents a query where you have to find the product of all powers[j] with lefti <= j <= righti.
Return an array answers, equal in length to queries, where answers[i] is the answer to the ith query. Since the answer to the ith query may be too large, each answers[i] should be returned modulo 109 + 7.
Example 1:
Input: n = 15, queries = [[0,1],[2,2],[0,3]]
Output: [2,4,64]
Explanation:
For n = 15, powers = [1,2,4,8]. It can be shown that powers cannot be a smaller size.
Answer to 1st query: powers[0] * powers[1] = 1 * 2 = 2.
Answer to 2nd query: powers[2] = 4.
Answer to 3rd query: powers[0] * powers[1] * powers[2] * powers[3] = 1 * 2 * 4 * 8 = 64.
Each answer modulo 109 + 7 yields the same answer, so [2,4,64] is returned.
Example 2:
Input: n = 2, queries = [[0,0]]
Output: [2]
Explanation: For n = 2, powers = [2]. The answer to the only query is powers[0] = 2. The answer modulo 109 + 7 is the same, so [2] is returned.
Constraints:
1 <= n <= 1091 <= queries.length <= 1050 <= starti <= endi < powers.length
Solution
@Suppress("NAME_SHADOWING")
class Solution {
fun productQueries(n: Int, queries: Array<IntArray>): IntArray {
val length = queries.size
val mod = (1e9 + 7).toLong()
// convert n to binary form
// take the set bit and find the corresponding 2^i
// now answer for the query
val powerTracker = IntArray(32)
val productTakingPowers: MutableList<Long> = ArrayList()
val result = IntArray(length)
fillPowerTracker(powerTracker, n)
fillProductTakingPowers(productTakingPowers, powerTracker)
var index = 0
for (query in queries) {
val left = query[0]
val right = query[1]
var product: Long = 1
for (i in left..right) {
product = product * productTakingPowers[i] % mod
}
result[index++] = (product % mod).toInt()
}
return result
}
private fun fillPowerTracker(powerTracker: IntArray, n: Int) {
var n = n
var index = 0
while (n > 0) {
powerTracker[index++] = n and 1
n = n shr 1
}
}
private fun fillProductTakingPowers(productTakingPowers: MutableList<Long>, powerTracker: IntArray) {
for (i in 0..31) {
if (powerTracker[i] == 1) {
val power = Math.pow(2.0, i.toDouble()).toLong()
productTakingPowers.add(power)
}
}
}
}