g2301_2400.s2376_count_special_integers.Solution.kt Maven / Gradle / Ivy

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Kotlin-based LeetCode algorithm problem solutions, regularly updated

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package g2301_2400.s2376_count_special_integers

// #Hard #Dynamic_Programming #Math #2023_07_02_Time_125_ms_(100.00%)_Space_32.8_MB_(100.00%)

@Suppress("NAME_SHADOWING")
class Solution {
    private lateinit var cntMap: IntArray
    // number n as an array, splitted by each digit
    private lateinit var digits: IntArray

    fun countSpecialNumbers(n: Int): Int {
        var n = n
        if (n < 10) {
            return n
        }
        val len = Math.log10(n.toDouble()).toInt() + 1
        cntMap = IntArray(len - 1)
        val res = countUnbounded(len)
        digits = IntArray(len)
        var i = len - 1
        while (i >= 0) {
            digits[i] = n % 10
            i--
            n /= 10
        }
        return res + dfs(0, 0)
    }

    private fun dfs(i: Int, mask: Int): Int {
        if (i == digits.size) {
            return 1
        }
        var res = 0
        val startJ = if (i == 0) 1 else 0
        for (j in startJ until digits[i]) {
            if (mask and (1 shl j) == 0) {
                // unbounded lens left
                val unbounded = digits.size - 2 - i
                res += if (unbounded >= 0) count(unbounded, 9 - i) else 1
            }
        }
        if (mask and (1 shl digits[i]) == 0) {
            res += dfs(i + 1, mask or (1 shl digits[i]))
        }
        return res
    }

    private fun count(i: Int, max: Int): Int {
        return if (i == 0) {
            max
        } else (max - i) * count(i - 1, max)
    }

    private fun countUnbounded(len: Int): Int {
        var res = 9
        cntMap[0] = 9
        for (i in 0 until len - 2) {
            cntMap[i + 1] = cntMap[i] * (9 - i)
            res += cntMap[i + 1]
        }
        return res
    }
}