LeetCode in Kotlin

1316. Distinct Echo Substrings

Hard

Return the number of distinct non-empty substrings of text that can be written as the concatenation of some string with itself (i.e. it can be written as a + a where a is some string).

Example 1:

Input: text = “abcabcabc”

Output: 3

Explanation: The 3 substrings are “abcabc”, “bcabca” and “cabcab”.

Example 2:

Input: text = “leetcodeleetcode”

Output: 2

Explanation: The 2 substrings are “ee” and “leetcodeleetcode”.

Constraints:

• 1 <= text.length <= 2000
• text has only lowercase English letters.

Solution

class Solution {
    fun distinctEchoSubstrings(text: String): Int {
        val n = text.length
        val dp = Array(n) { IntArray(n) }
        for (i in 0 until n) {
            var hash: Long = 0
            for (j in i until n) {
                hash = hash * PRIME + (text[j].code - 'a'.code + 1)
                hash %= MOD.toLong()
                dp[i][j] = hash.toInt()
            }
        }
        val set: MutableSet<Int> = HashSet()
        var res = 0
        for (i in 0 until n - 1) {
            var j = i
            while (2 * j - i + 1 < n) {
                if (dp[i][j] == dp[j + 1][2 * j - i + 1] && set.add(dp[i][j])) {
                    res++
                }
                j++
            }
        }
        return res
    }

    companion object {
        private const val PRIME = 101
        private const val MOD = 1000000007
    }
}

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