Added tasks 3324-3327

src/main/kotlin/g3301_3400/s3324_find_the_sequence_of_strings_appeared_on_the_screen/Solution.kt

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+package g3301_3400.s3324_find_the_sequence_of_strings_appeared_on_the_screen
+
+// #Medium #String #Simulation #2024_10_22_Time_8_ms_(100.00%)_Space_62.7_MB_(29.63%)
+
+class Solution {
+    fun stringSequence(target: String): List<String> {
+        val ans: MutableList<String> = ArrayList<String>()
+        val l = target.length
+        val cur = StringBuilder()
+        for (i in 0 until l) {
+            val tCh = target[i]
+            cur.append('a')
+            ans.add(cur.toString())
+            while (cur[i] != tCh) {
+                val lastCh = cur[i]
+                val nextCh = (if (lastCh == 'z') 'a'.code else lastCh.code + 1).toChar()
+                cur.setCharAt(i, nextCh)
+                ans.add(cur.toString())
+            }
+        }
+        return ans
+    }
+}

src/main/kotlin/g3301_3400/s3324_find_the_sequence_of_strings_appeared_on_the_screen/readme.md

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+3324\. Find the Sequence of Strings Appeared on the Screen
+
+Medium
+
+You are given a string `target`.
+
+Alice is going to type `target` on her computer using a special keyboard that has **only two** keys:
+
+*   Key 1 appends the character `"a"` to the string on the screen.
+*   Key 2 changes the **last** character of the string on the screen to its **next** character in the English alphabet. For example, `"c"` changes to `"d"` and `"z"` changes to `"a"`.
+
+**Note** that initially there is an _empty_ string `""` on the screen, so she can **only** press key 1.
+
+Return a list of _all_ strings that appear on the screen as Alice types `target`, in the order they appear, using the **minimum** key presses.
+
+**Example 1:**
+
+**Input:** target = "abc"
+
+**Output:** ["a","aa","ab","aba","abb","abc"]
+
+**Explanation:**
+
+The sequence of key presses done by Alice are:
+
+*   Press key 1, and the string on the screen becomes `"a"`.
+*   Press key 1, and the string on the screen becomes `"aa"`.
+*   Press key 2, and the string on the screen becomes `"ab"`.
+*   Press key 1, and the string on the screen becomes `"aba"`.
+*   Press key 2, and the string on the screen becomes `"abb"`.
+*   Press key 2, and the string on the screen becomes `"abc"`.
+
+**Example 2:**
+
+**Input:** target = "he"
+
+**Output:** ["a","b","c","d","e","f","g","h","ha","hb","hc","hd","he"]
+
+**Constraints:**
+
+*   `1 <= target.length <= 400`
+*   `target` consists only of lowercase English letters.

src/main/kotlin/g3301_3400/s3325_count_substrings_with_k_frequency_characters_i/Solution.kt

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+package g3301_3400.s3325_count_substrings_with_k_frequency_characters_i
+
+// #Medium #String #Hash_Table #Sliding_Window #2024_10_22_Time_3_ms_(88.00%)_Space_35.9_MB_(76.00%)
+
+class Solution {
+    fun numberOfSubstrings(s: String, k: Int): Int {
+        var left = 0
+        var result = 0
+        val count = IntArray(26)
+        for (i in 0 until s.length) {
+            val ch = s[i]
+            count[ch.code - 'a'.code]++
+
+            while (count[ch.code - 'a'.code] == k) {
+                result += s.length - i
+                val atLeft = s[left]
+                count[atLeft.code - 'a'.code]--
+                left++
+            }
+        }
+        return result
+    }
+}

src/main/kotlin/g3301_3400/s3325_count_substrings_with_k_frequency_characters_i/readme.md

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+3325\. Count Substrings With K-Frequency Characters I
+
+Medium
+
+Given a string `s` and an integer `k`, return the total number of substrings of `s` where **at least one** character appears **at least** `k` times.
+
+**Example 1:**
+
+**Input:** s = "abacb", k = 2
+
+**Output:** 4
+
+**Explanation:**
+
+The valid substrings are:
+
+*   `"aba"` (character `'a'` appears 2 times).
+*   `"abac"` (character `'a'` appears 2 times).
+*   `"abacb"` (character `'a'` appears 2 times).
+*   `"bacb"` (character `'b'` appears 2 times).
+
+**Example 2:**
+
+**Input:** s = "abcde", k = 1
+
+**Output:** 15
+
+**Explanation:**
+
+All substrings are valid because every character appears at least once.
+
+**Constraints:**
+
+*   `1 <= s.length <= 3000`
+*   `1 <= k <= s.length`
+*   `s` consists only of lowercase English letters.

src/main/kotlin/g3301_3400/s3326_minimum_division_operations_to_make_array_non_decreasing/Solution.kt

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+package g3301_3400.s3326_minimum_division_operations_to_make_array_non_decreasing
+
+// #Medium #Array #Math #Greedy #Number_Theory
+// #2024_10_22_Time_24_ms_(94.12%)_Space_64.2_MB_(64.71%)
+
+import kotlin.math.max
+
+class Solution {
+    fun minOperations(nums: IntArray): Int {
+        compute()
+        var op = 0
+        val n = nums.size
+        for (i in n - 2 downTo 0) {
+            while (nums[i] > nums[i + 1]) {
+                if (SIEVE[nums[i]] == 0) {
+                    return -1
+                }
+                nums[i] /= SIEVE[nums[i]]
+                op++
+            }
+            if (nums[i] > nums[i + 1]) {
+                return -1
+            }
+        }
+        return op
+    }
+
+    companion object {
+        private const val MAXI = 1000001
+        private val SIEVE = IntArray(MAXI)
+        private var precompute = false
+
+        private fun compute() {
+            if (precompute) {
+                return
+            }
+            for (i in 2 until MAXI) {
+                if (i * i > MAXI) {
+                    break
+                }
+                var j = i * i
+                while (j < MAXI) {
+                    SIEVE[j] =
+                        max(SIEVE[j], max(i, (j / i)))
+                    j += i
+                }
+            }
+            precompute = true
+        }
+    }
+}

src/main/kotlin/g3301_3400/s3326_minimum_division_operations_to_make_array_non_decreasing/readme.md

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+3326\. Minimum Division Operations to Make Array Non Decreasing
+
+Medium
+
+You are given an integer array `nums`.
+
+Any **positive** divisor of a natural number `x` that is **strictly less** than `x` is called a **proper divisor** of `x`. For example, 2 is a _proper divisor_ of 4, while 6 is not a _proper divisor_ of 6.
+
+You are allowed to perform an **operation** any number of times on `nums`, where in each **operation** you select any _one_ element from `nums` and divide it by its **greatest** **proper divisor**.
+
+Return the **minimum** number of **operations** required to make the array **non-decreasing**.
+
+If it is **not** possible to make the array _non-decreasing_ using any number of operations, return `-1`.
+
+**Example 1:**
+
+**Input:** nums = [25,7]
+
+**Output:** 1
+
+**Explanation:**
+
+Using a single operation, 25 gets divided by 5 and `nums` becomes `[5, 7]`.
+
+**Example 2:**
+
+**Input:** nums = [7,7,6]
+
+**Output:** \-1
+
+**Example 3:**
+
+**Input:** nums = [1,1,1,1]
+
+**Output:** 0
+
+**Constraints:**
+
+*   <code>1 <= nums.length <= 10<sup>5</sup></code>
+*   <code>1 <= nums[i] <= 10<sup>6</sup></code>

src/main/kotlin/g3301_3400/s3327_check_if_dfs_strings_are_palindromes/Solution.kt

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+package g3301_3400.s3327_check_if_dfs_strings_are_palindromes
+
+// #Hard #Array #String #Hash_Table #Depth_First_Search #Tree #Hash_Function
+// #2024_10_22_Time_165_ms_(100.00%)_Space_88.9_MB_(66.67%)
+
+import kotlin.math.min
+
+class Solution {
+    private val e: MutableList<MutableList<Int?>?> = ArrayList<MutableList<Int?>?>()
+    private val stringBuilder = StringBuilder()
+    private var s: String? = null
+    private var now = 0
+    private var n = 0
+    private lateinit var l: IntArray
+    private lateinit var r: IntArray
+    private lateinit var p: IntArray
+    private lateinit var c: CharArray
+
+    private fun dfs(x: Int) {
+        l[x] = now + 1
+        for (v in e[x]!!) {
+            dfs(v!!)
+        }
+        stringBuilder.append(s!![x])
+        r[x] = ++now
+    }
+
+    private fun matcher() {
+        c[0] = '~'
+        c[1] = '#'
+        for (i in 1..n) {
+            c[2 * i + 1] = '#'
+            c[2 * i] = stringBuilder[i - 1]
+        }
+        var j = 1
+        var mid = 0
+        var localR = 0
+        while (j <= 2 * n + 1) {
+            if (j <= localR) {
+                p[j] = min(p[(mid shl 1) - j], (localR - j + 1))
+            }
+            while (c[j - p[j]] == c[j + p[j]]) {
+                ++p[j]
+            }
+            if (p[j] + j > localR) {
+                localR = p[j] + j - 1
+                mid = j
+            }
+            ++j
+        }
+    }
+
+    fun findAnswer(parent: IntArray, s: String): BooleanArray {
+        n = parent.size
+        this.s = s
+        for (i in 0 until n) {
+            e.add(ArrayList<Int?>())
+        }
+        for (i in 1 until n) {
+            e[parent[i]]!!.add(i)
+        }
+        l = IntArray(n)
+        r = IntArray(n)
+        dfs(0)
+        c = CharArray(2 * n + 10)
+        p = IntArray(2 * n + 10)
+        matcher()
+        val ans = BooleanArray(n)
+        for (i in 0 until n) {
+            val mid = (2 * r[i] - 2 * l[i] + 1) / 2 + 2 * l[i]
+            ans[i] = p[mid] - 1 >= r[i] - l[i] + 1
+        }
+        return ans
+    }
+}

src/main/kotlin/g3301_3400/s3327_check_if_dfs_strings_are_palindromes/readme.md

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+3327\. Check if DFS Strings Are Palindromes
+
+Hard
+
+You are given a tree rooted at node 0, consisting of `n` nodes numbered from `0` to `n - 1`. The tree is represented by an array `parent` of size `n`, where `parent[i]` is the parent of node `i`. Since node 0 is the root, `parent[0] == -1`.
+
+You are also given a string `s` of length `n`, where `s[i]` is the character assigned to node `i`.
+
+Consider an empty string `dfsStr`, and define a recursive function `dfs(int x)` that takes a node `x` as a parameter and performs the following steps in order:
+
+*   Iterate over each child `y` of `x` **in increasing order of their numbers**, and call `dfs(y)`.
+*   Add the character `s[x]` to the end of the string `dfsStr`.
+
+**Note** that `dfsStr` is shared across all recursive calls of `dfs`.
+
+You need to find a boolean array `answer` of size `n`, where for each index `i` from `0` to `n - 1`, you do the following:
+
+*   Empty the string `dfsStr` and call `dfs(i)`.
+*   If the resulting string `dfsStr` is a **palindrome**, then set `answer[i]` to `true`. Otherwise, set `answer[i]` to `false`.
+
+Return the array `answer`.
+
+A **palindrome** is a string that reads the same forward and backward.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2024/09/01/tree1drawio.png)
+
+**Input:** parent = [-1,0,0,1,1,2], s = "aababa"
+
+**Output:** [true,true,false,true,true,true]
+
+**Explanation:**
+
+*   Calling `dfs(0)` results in the string `dfsStr = "abaaba"`, which is a palindrome.
+*   Calling `dfs(1)` results in the string `dfsStr = "aba"`, which is a palindrome.
+*   Calling `dfs(2)` results in the string `dfsStr = "ab"`, which is **not** a palindrome.
+*   Calling `dfs(3)` results in the string `dfsStr = "a"`, which is a palindrome.
+*   Calling `dfs(4)` results in the string `dfsStr = "b"`, which is a palindrome.
+*   Calling `dfs(5)` results in the string `dfsStr = "a"`, which is a palindrome.
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2024/09/01/tree2drawio-1.png)
+
+**Input:** parent = [-1,0,0,0,0], s = "aabcb"
+
+**Output:** [true,true,true,true,true]
+
+**Explanation:**
+
+Every call on `dfs(x)` results in a palindrome string.
+
+**Constraints:**
+
+*   `n == parent.length == s.length`
+*   <code>1 <= n <= 10<sup>5</sup></code>
+*   `0 <= parent[i] <= n - 1` for all `i >= 1`.
+*   `parent[0] == -1`
+*   `parent` represents a valid tree.
+*   `s` consists only of lowercase English letters.

src/test/kotlin/g3301_3400/s3324_find_the_sequence_of_strings_appeared_on_the_screen/SolutionTest.kt

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+package g3301_3400.s3324_find_the_sequence_of_strings_appeared_on_the_screen
+
+import org.hamcrest.CoreMatchers.equalTo
+import org.hamcrest.MatcherAssert.assertThat
+import org.junit.jupiter.api.Test
+
+internal class SolutionTest {
+    @Test
+    fun stringSequence() {
+        assertThat<List<String>>(
+            Solution().stringSequence("abc"),
+            equalTo<List<String>>(listOf<String>("a", "aa", "ab", "aba", "abb", "abc"))
+        )
+    }
+
+    @Test
+    fun stringSequence2() {
+        assertThat<List<String>>(
+            Solution().stringSequence("he"),
+            equalTo<List<String>>(
+                listOf<String>(
+                    "a", "b", "c", "d", "e", "f", "g", "h", "ha", "hb", "hc", "hd",
+                    "he"
+                )
+            )
+        )
+    }
+}