LeetCode in Kotlin
1416. Restore The Array
Hard
A program was supposed to print an array of integers. The program forgot to print whitespaces and the array is printed as a string of digits s and all we know is that all integers in the array were in the range [1, k] and there are no leading zeros in the array.
Given the string s and the integer k, return the number of the possible arrays that can be printed as s using the mentioned program. Since the answer may be very large, return it modulo 109 + 7.
Example 1:
Input: s = “1000”, k = 10000
Output: 1
Explanation: The only possible array is [1000]
Example 2:
Input: s = “1000”, k = 10
Output: 0
Explanation: There cannot be an array that was printed this way and has all integer >= 1 and <= 10.
Example 3:
Input: s = “1317”, k = 2000
Output: 8
Explanation: Possible arrays are [1317],[131,7],[13,17],[1,317],[13,1,7],[1,31,7],[1,3,17],[1,3,1,7]
Constraints:
1 <= s.length <= 105sconsists of only digits and does not contain leading zeros.1 <= k <= 109
Solution
class Solution {
fun numberOfArrays(s: String, k: Int): Int {
// dp[i] is number of ways to print valid arrays from string s start at i
val dp = arrayOfNulls<Int>(s.length)
return dfs(s, k.toLong(), 0, dp)
}
private fun dfs(s: String, k: Long, i: Int, dp: Array<Int?>): Int {
// base case -> Found a valid way
if (i == s.length) return 1
// all numbers are in range [1, k] and there are no leading zeros -> So numbers starting with 0 mean invalid!
if (s[i] == '0') return 0
if (dp[i] != null) return dp[i]!!
var ans = 0
var num: Long = 0
for (j in i until s.length) {
// num is the value of the substring s[i..j]
num = num * 10 + s[j].code.toLong() - '0'.code.toLong()
// num must be in range [1, k]
if (num > k) break
ans += dfs(s, k, j + 1, dp)
ans %= 1000000007
}
return ans.also { dp[i] = it }
}
}