Added tasks 3722-3729

src/main/kotlin/g3701_3800/s3722_lexicographically_smallest_string_after_reverse/Solution.kt

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+package g3701_3800.s3722_lexicographically_smallest_string_after_reverse
+
+// #Medium #Binary_Search #Two_Pointers #Enumeration #Biweekly_Contest_168
+// #2025_10_28_Time_8_ms_(100.00%)_Space_45.74_MB_(100.00%)
+
+class Solution {
+    fun lexSmallest(s: String): String {
+        val n = s.length
+        val arr = s.toCharArray()
+        val best = arr.clone()
+        // Check all reverse first k operations
+        for (k in 1..n) {
+            if (isBetterReverseFirstK(arr, k, best)) {
+                updateBestReverseFirstK(arr, k, best)
+            }
+        }
+        // Check all reverse last k operations
+        for (k in 1..n) {
+            if (isBetterReverseLastK(arr, k, best)) {
+                updateBestReverseLastK(arr, k, best)
+            }
+        }
+        return String(best)
+    }
+
+    private fun isBetterReverseFirstK(arr: CharArray, k: Int, best: CharArray): Boolean {
+        for (i in arr.indices) {
+            val currentChar = if (i < k) arr[k - 1 - i] else arr[i]
+            if (currentChar < best[i]) {
+                return true
+            }
+            if (currentChar > best[i]) {
+                return false
+            }
+        }
+        return false
+    }
+
+    private fun isBetterReverseLastK(arr: CharArray, k: Int, best: CharArray): Boolean {
+        val n = arr.size
+        for (i in 0..<n) {
+            val currentChar = if (i < n - k) arr[i] else arr[n - 1 - (i - (n - k))]
+            if (currentChar < best[i]) {
+                return true
+            }
+            if (currentChar > best[i]) {
+                return false
+            }
+        }
+        return false
+    }
+
+    private fun updateBestReverseFirstK(arr: CharArray, k: Int, best: CharArray) {
+        for (i in 0..<k) {
+            best[i] = arr[k - 1 - i]
+        }
+        if (arr.size - k >= 0) {
+            System.arraycopy(arr, k, best, k, arr.size - k)
+        }
+    }
+
+    private fun updateBestReverseLastK(arr: CharArray, k: Int, best: CharArray) {
+        val n = arr.size
+        if (n - k >= 0) {
+            System.arraycopy(arr, 0, best, 0, n - k)
+        }
+        for (i in 0..<k) {
+            best[n - k + i] = arr[n - 1 - i]
+        }
+    }
+}

src/main/kotlin/g3701_3800/s3722_lexicographically_smallest_string_after_reverse/readme.md

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+3722\. Lexicographically Smallest String After Reverse
+
+Medium
+
+You are given a string `s` of length `n` consisting of lowercase English letters.
+
+You must perform **exactly** one operation by choosing any integer `k` such that `1 <= k <= n` and either:
+
+*   reverse the **first** `k` characters of `s`, or
+*   reverse the **last** `k` characters of `s`.
+
+Return the **lexicographically smallest** string that can be obtained after **exactly** one such operation.
+
+A string `a` is **lexicographically smaller** than a string `b` if, at the first position where they differ, `a` has a letter that appears earlier in the alphabet than the corresponding letter in `b`. If the first `min(a.length, b.length)` characters are the same, then the shorter string is considered lexicographically smaller.
+
+**Example 1:**
+
+**Input:** s = "dcab"
+
+**Output:** "acdb"
+
+**Explanation:**
+
+*   Choose `k = 3`, reverse the first 3 characters.
+*   Reverse `"dca"` to `"acd"`, resulting string `s = "acdb"`, which is the lexicographically smallest string achievable.
+
+**Example 2:**
+
+**Input:** s = "abba"
+
+**Output:** "aabb"
+
+**Explanation:**
+
+*   Choose `k = 3`, reverse the last 3 characters.
+*   Reverse `"bba"` to `"abb"`, so the resulting string is `"aabb"`, which is the lexicographically smallest string achievable.
+
+**Example 3:**
+
+**Input:** s = "zxy"
+
+**Output:** "xzy"
+
+**Explanation:**
+
+*   Choose `k = 2`, reverse the first 2 characters.
+*   Reverse `"zx"` to `"xz"`, so the resulting string is `"xzy"`, which is the lexicographically smallest string achievable.
+
+**Constraints:**
+
+*   `1 <= n == s.length <= 1000`
+*   `s` consists of lowercase English letters.

src/main/kotlin/g3701_3800/s3723_maximize_sum_of_squares_of_digits/Solution.kt

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+package g3701_3800.s3723_maximize_sum_of_squares_of_digits
+
+// #Medium #Math #Greedy #Biweekly_Contest_168
+// #2025_10_28_Time_16_ms_(94.44%)_Space_47.62_MB_(61.11%)
+
+class Solution {
+    fun maxSumOfSquares(places: Int, sum: Int): String {
+        var ans = ""
+        val nines = sum / 9
+        if (places < nines) {
+            return ans
+        } else if (places == nines) {
+            val remSum = sum - nines * 9
+            if (remSum > 0) {
+                return ans
+            }
+            ans = "9".repeat(nines)
+        } else {
+            val remSum = sum - nines * 9
+            ans = "9".repeat(nines) + remSum
+            val extra = places - ans.length
+            if (extra > 0) {
+                ans = ans + ("0".repeat(extra))
+            }
+        }
+        return ans
+    }
+}

src/main/kotlin/g3701_3800/s3723_maximize_sum_of_squares_of_digits/readme.md

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+3723\. Maximize Sum of Squares of Digits
+
+Medium
+
+You are given two **positive** integers `num` and `sum`.
+
+A positive integer `n` is **good** if it satisfies both of the following:
+
+*   The number of digits in `n` is **exactly** `num`.
+*   The sum of digits in `n` is **exactly** `sum`.
+
+The **score** of a **good** integer `n` is the sum of the squares of digits in `n`.
+
+Return a **string** denoting the **good** integer `n` that achieves the **maximum** **score**. If there are multiple possible integers, return the **maximum** one. If no such integer exists, return an empty string.
+
+**Example 1:**
+
+**Input:** num = 2, sum = 3
+
+**Output:** "30"
+
+**Explanation:**
+
+There are 3 good integers: 12, 21, and 30.
+
+*   The score of 12 is <code>1<sup>2</sup> + 2<sup>2</sup> = 5</code>.
+*   The score of 21 is <code>2<sup>2</sup> + 1<sup>2</sup> = 5</code>.
+*   The score of 30 is <code>3<sup>2</sup> + 0<sup>2</sup> = 9</code>.
+
+The maximum score is 9, which is achieved by the good integer 30. Therefore, the answer is `"30"`.
+
+**Example 2:**
+
+**Input:** num = 2, sum = 17
+
+**Output:** "98"
+
+**Explanation:**
+
+There are 2 good integers: 89 and 98.
+
+*   The score of 89 is <code>8<sup>2</sup> + 9<sup>2</sup> = 145</code>.
+*   The score of 98 is <code>9<sup>2</sup> + 8<sup>2</sup> = 145</code>.
+
+The maximum score is 145. The maximum good integer that achieves this score is 98. Therefore, the answer is `"98"`.
+
+**Example 3:**
+
+**Input:** num = 1, sum = 10
+
+**Output:** ""
+
+**Explanation:**
+
+There are no integers that have exactly 1 digit and whose digits sum to 10. Therefore, the answer is `""`.
+
+**Constraints:**
+
+*   <code>1 <= num <= 2 * 10<sup>5</sup></code>
+*   <code>1 <= sum <= 2 * 10<sup>6</sup></code>

src/main/kotlin/g3701_3800/s3724_minimum_operations_to_transform_array/Solution.kt

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+package g3701_3800.s3724_minimum_operations_to_transform_array
+
+// #Medium #Array #Greedy #Biweekly_Contest_168
+// #2025_10_28_Time_10_ms_(83.33%)_Space_66.99_MB_(100.00%)
+
+import kotlin.math.abs
+import kotlin.math.max
+import kotlin.math.min
+
+class Solution {
+    fun minOperations(nums1: IntArray, nums2: IntArray): Long {
+        val n = nums1.size
+        val last = nums2[n]
+        var steps: Long = 1
+        var minDiffFromLast = Long.MAX_VALUE
+        for (i in 0..<n) {
+            val min = min(nums1[i], nums2[i])
+            val max = max(nums1[i], nums2[i])
+            steps += abs(max - min).toLong()
+            if (minDiffFromLast > 0) {
+                if (min <= last && last <= max) {
+                    minDiffFromLast = 0
+                } else {
+                    minDiffFromLast = min(
+                        minDiffFromLast,
+                        min(abs(min - last), abs(max - last)).toLong(),
+                    )
+                }
+            }
+        }
+        return steps + minDiffFromLast
+    }
+}

src/main/kotlin/g3701_3800/s3724_minimum_operations_to_transform_array/readme.md

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+3724\. Minimum Operations to Transform Array
+
+Medium
+
+You are given two integer arrays `nums1` of length `n` and `nums2` of length `n + 1`.
+
+You want to transform `nums1` into `nums2` using the **minimum** number of operations.
+
+You may perform the following operations **any** number of times, each time choosing an index `i`:
+
+*   **Increase** `nums1[i]` by 1.
+*   **Decrease** `nums1[i]` by 1.
+*   **Append** `nums1[i]` to the **end** of the array.
+
+Return the **minimum** number of operations required to transform `nums1` into `nums2`.
+
+**Example 1:**
+
+**Input:** nums1 = [2,8], nums2 = [1,7,3]
+
+**Output:** 4
+
+**Explanation:**
+
+| Step | `i` | Operation | `nums1[i]` | Updated `nums1` |
+|------|------|------------|-------------|----------------|
+| 1 | 0 | Append | - | [2, 8, 2] |
+| 2 | 0 | Decrement | Decreases to 1 | [1, 8, 2] |
+| 3 | 1 | Decrement | Decreases to 7 | [1, 7, 2] |
+| 4 | 2 | Increment | Increases to 3 | [1, 7, 3] |
+
+Thus, after 4 operations `nums1` is transformed into `nums2`.
+
+**Example 2:**
+
+**Input:** nums1 = [1,3,6], nums2 = [2,4,5,3]
+
+**Output:** 4
+
+**Explanation:**
+
+| Step | `i` | Operation | `nums1[i]` | Updated `nums1` |
+|------|------|------------|-------------|----------------|
+| 1 | 1 | Append | - | [1, 3, 6, 3] |
+| 2 | 0 | Increment | Increases to 2 | [2, 3, 6, 3] |
+| 3 | 1 | Increment | Increases to 4 | [2, 4, 6, 3] |
+| 4 | 2 | Decrement | Decreases to 5 | [2, 4, 5, 3] |
+
+Thus, after 4 operations `nums1` is transformed into `nums2`.
+
+**Example 3:**
+
+**Input:** nums1 = [2], nums2 = [3,4]
+
+**Output:** 3
+
+**Explanation:**
+
+| Step | `i` | Operation | `nums1[i]` | Updated `nums1` |
+|------|------|------------|-------------|----------------|
+| 1 | 0 | Increment | Increases to 3 | [3] |
+| 2 | 0 | Append | - | [3, 3] |
+| 3 | 1 | Increment | Increases to 4 | [3, 4] |
+
+Thus, after 3 operations `nums1` is transformed into `nums2`.
+
+**Constraints:**
+
+*   <code>1 <= n == nums1.length <= 10<sup>5</sup></code>
+*   `nums2.length == n + 1`
+*   <code>1 <= nums1[i], nums2[i] <= 10<sup>5</sup></code>

src/main/kotlin/g3701_3800/s3725_count_ways_to_choose_coprime_integers_from_rows/Solution.kt

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+package g3701_3800.s3725_count_ways_to_choose_coprime_integers_from_rows
+
+// #Hard #Array #Dynamic_Programming #Math #Matrix #Number_Theory #Combinatorics
+// #Biweekly_Contest_168 #2025_10_28_Time_29_ms_(100.00%)_Space_51.80_MB_(100.00%)
+
+import kotlin.math.max
+
+class Solution {
+    fun countCoprime(mat: Array<IntArray>): Int {
+        val m = mat.size
+        val n = mat[0].size
+        var maxVal = 0
+        for (ints in mat) {
+            for (j in 0..<n) {
+                maxVal = max(maxVal, ints[j])
+            }
+        }
+        val gcdWays: MutableMap<Int, Long> = HashMap()
+        for (g in maxVal downTo 1) {
+            var ways = countWaysWithDivisor(mat, g, m, n)
+            if (ways > 0) {
+                var multiple = 2 * g
+                while (multiple <= maxVal) {
+                    if (gcdWays.containsKey(multiple)) {
+                        ways = (ways - gcdWays[multiple]!! + MOD) % MOD
+                    }
+                    multiple += g
+                }
+                gcdWays[g] = ways
+            }
+        }
+        return gcdWays.getOrDefault(1, 0L).toInt()
+    }
+
+    private fun countWaysWithDivisor(matrix: Array<IntArray>, divisor: Int, rows: Int, cols: Int): Long {
+        var totalWays: Long = 1
+        for (row in 0..<rows) {
+            var validChoices = 0
+            for (col in 0..<cols) {
+                if (matrix[row][col] % divisor == 0) {
+                    validChoices++
+                }
+            }
+            if (validChoices == 0) {
+                return 0
+            }
+            totalWays = (totalWays * validChoices) % MOD
+        }
+        return totalWays
+    }
+
+    companion object {
+        private const val MOD = 1000000007
+    }
+}