LeetCode in Kotlin
552. Student Attendance Record II
Hard
An attendance record for a student can be represented as a string where each character signifies whether the student was absent, late, or present on that day. The record only contains the following three characters:
'A': Absent.'L': Late.'P': Present.
Any student is eligible for an attendance award if they meet both of the following criteria:
- The student was absent (
'A') for strictly fewer than 2 days total. - The student was never late (
'L') for 3 or more consecutive days.
Given an integer n, return the number of possible attendance records of length n that make a student eligible for an attendance award. The answer may be very large, so return it modulo 109 + 7.
Example 1:
Input: n = 2
Output: 8
Explanation: There are 8 records with length 2 that are eligible for an award: “PP”, “AP”, “PA”, “LP”, “PL”, “AL”, “LA”, “LL” Only “AA” is not eligible because there are 2 absences (there need to be fewer than 2).
Example 2:
Input: n = 1
Output: 3
Example 3:
Input: n = 10101
Output: 183236316
Constraints:
1 <= n <= 105
Solution
@Suppress("NAME_SHADOWING")
class Solution {
fun checkRecord(n: Int): Int {
if (n == 0 || n == 1 || n == 2) {
return n * 3 + n * (n - 1)
}
val mod: Long = 1000000007
val matrix = arrayOf(
longArrayOf(1, 1, 0, 1, 0, 0),
longArrayOf(1, 0, 1, 1, 0, 0),
longArrayOf(1, 0, 0, 1, 0, 0),
longArrayOf(0, 0, 0, 1, 1, 0),
longArrayOf(0, 0, 0, 1, 0, 1),
longArrayOf(0, 0, 0, 1, 0, 0),
)
val e = quickPower(matrix, n - 1)
return (
(e[0].sum() + e[1].sum() + e[3].sum()) %
mod
).toInt()
}
private fun quickPower(a: Array<LongArray>, times: Int): Array<LongArray> {
var a = a
var times = times
val n = a.size
var e = Array(n) { LongArray(n) }
for (i in 0 until n) {
e[i][i] = 1
}
while (times != 0) {
if (times % 2 == 1) {
e = multiple(e, a, n)
}
times = times shr 1
a = multiple(a, a, n)
}
return e
}
private fun multiple(a: Array<LongArray>, b: Array<LongArray>, n: Int): Array<LongArray> {
val target = Array(n) { LongArray(n) }
for (j in 0 until n) {
for (k in 0 until n) {
for (l in 0 until n) {
target[j][k] += a[j][l] * b[l][k]
target[j][k] = target[j][k] % 1000000007
}
}
}
return target
}
}