LeetCode in Kotlin
940. Distinct Subsequences II
Hard
Given a string s, return the number of distinct non-empty subsequences of s. Since the answer may be very large, return it modulo 109 + 7.
A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not.
Example 1:
Input: s = “abc”
Output: 7
Explanation: The 7 distinct subsequences are “a”, “b”, “c”, “ab”, “ac”, “bc”, and “abc”.
Example 2:
Input: s = “aba”
Output: 6
Explanation: The 6 distinct subsequences are “a”, “b”, “ab”, “aa”, “ba”, and “aba”.
Example 3:
Input: s = “aaa”
Output: 3
Explanation: The 3 distinct subsequences are “a”, “aa” and “aaa”.
Constraints:
1 <= s.length <= 2000sconsists of lowercase English letters.
Solution
class Solution {
fun distinctSubseqII(s: String): Int {
val n = s.length
val mod = 1000000007
val arr = IntArray(26)
for (i in 0 until n) {
val x = s[i].code - 'a'.code
var sum: Long = 0
arr[x] += 1
for (j in 0..25) {
sum = (sum + arr[j]) % mod
}
arr[x] = sum.toInt()
}
var total: Long = 0
for (x in arr) {
total = (total + x) % mod
}
return total.toInt()
}
}