Added tasks 3248-3251

src/main/kotlin/g3201_3300/s3248_snake_in_matrix/Solution.kt

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+package g3201_3300.s3248_snake_in_matrix
+
+// #Easy #Array #String #Simulation #2024_08_13_Time_174_ms_(90.91%)_Space_37.5_MB_(34.09%)
+
+class Solution {
+    fun finalPositionOfSnake(n: Int, commands: List<String>): Int {
+        var x = 0
+        var y = 0
+        for (command in commands) {
+            when (command) {
+                "UP" -> if (x > 0) {
+                    x--
+                }
+                "DOWN" -> if (x < n - 1) {
+                    x++
+                }
+                "LEFT" -> if (y > 0) {
+                    y--
+                }
+                "RIGHT" -> if (y < n - 1) {
+                    y++
+                }
+            }
+        }
+        return (x * n) + y
+    }
+}

src/main/kotlin/g3201_3300/s3248_snake_in_matrix/readme.md

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+3248\. Snake in Matrix
+
+Easy
+
+There is a snake in an `n x n` matrix `grid` and can move in **four possible directions**. Each cell in the `grid` is identified by the position: `grid[i][j] = (i * n) + j`.
+
+The snake starts at cell 0 and follows a sequence of commands.
+
+You are given an integer `n` representing the size of the `grid` and an array of strings `commands` where each `command[i]` is either `"UP"`, `"RIGHT"`, `"DOWN"`, and `"LEFT"`. It's guaranteed that the snake will remain within the `grid` boundaries throughout its movement.
+
+Return the position of the final cell where the snake ends up after executing `commands`.
+
+**Example 1:**
+
+**Input:** n = 2, commands = ["RIGHT","DOWN"]
+
+**Output:** 3
+
+**Explanation:**
+
+![image](image01.png)
+
+**Example 2:**
+
+**Input:** n = 3, commands = ["DOWN","RIGHT","UP"]
+
+**Output:** 1
+
+**Explanation:**
+
+![image](image02.png)
+
+**Constraints:**
+
+*   `2 <= n <= 10`
+*   `1 <= commands.length <= 100`
+*   `commands` consists only of `"UP"`, `"RIGHT"`, `"DOWN"`, and `"LEFT"`.
+*   The input is generated such the snake will not move outside of the boundaries.

src/main/kotlin/g3201_3300/s3249_count_the_number_of_good_nodes/Solution.kt

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+package g3201_3300.s3249_count_the_number_of_good_nodes
+
+// #Medium #Depth_First_Search #Tree #2024_08_13_Time_1190_ms_(100.00%)_Space_127.6_MB_(77.27%)
+
+class Solution {
+    private var count = 0
+
+    fun countGoodNodes(edges: Array<IntArray>): Int {
+        val n = edges.size + 1
+        val nodes = arrayOfNulls<TNode>(n)
+        nodes[0] = TNode()
+        for (edge in edges) {
+            val a = edge[0]
+            val b = edge[1]
+            if (nodes[b] != null && nodes[a] == null) {
+                nodes[a] = TNode()
+                nodes[b]!!.children.add(nodes[a])
+            } else {
+                if (nodes[a] == null) {
+                    nodes[a] = TNode()
+                }
+                if (nodes[b] == null) {
+                    nodes[b] = TNode()
+                }
+                nodes[a]!!.children.add(nodes[b])
+            }
+        }
+        sizeOfTree(nodes[0])
+        return count
+    }
+
+    private fun sizeOfTree(node: TNode?): Int {
+        if (node!!.size > 0) {
+            return node.size
+        }
+        val children: List<TNode?> = node.children
+        if (children.isEmpty()) {
+            count++
+            node.size = 1
+            return 1
+        }
+        val size = sizeOfTree(children[0])
+        var sum = size
+        var goodNode = true
+        for (i in 1 until children.size) {
+            val child = children[i]
+            if (size != sizeOfTree(child)) {
+                goodNode = false
+            }
+            sum += sizeOfTree(child)
+        }
+        if (goodNode) {
+            count++
+        }
+        sum++
+        node.size = sum
+        return sum
+    }
+
+    private class TNode {
+        var size: Int = -1
+        var children: MutableList<TNode?> = ArrayList()
+    }
+}

src/main/kotlin/g3201_3300/s3249_count_the_number_of_good_nodes/readme.md

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+3249\. Count the Number of Good Nodes
+
+Medium
+
+There is an **undirected** tree with `n` nodes labeled from `0` to `n - 1`, and rooted at node `0`. You are given a 2D integer array `edges` of length `n - 1`, where <code>edges[i] = [a<sub>i</sub>, b<sub>i</sub>]</code> indicates that there is an edge between nodes <code>a<sub>i</sub></code> and <code>b<sub>i</sub></code> in the tree.
+
+A node is **good** if all the subtrees rooted at its children have the same size.
+
+Return the number of **good** nodes in the given tree.
+
+A **subtree** of `treeName` is a tree consisting of a node in `treeName` and all of its descendants.
+
+**Example 1:**
+
+**Input:** edges = [[0,1],[0,2],[1,3],[1,4],[2,5],[2,6]]
+
+**Output:** 7
+
+**Explanation:**
+
+![](https://assets.leetcode.com/uploads/2024/05/26/tree1.png)
+
+All of the nodes of the given tree are good.
+
+**Example 2:**
+
+**Input:** edges = [[0,1],[1,2],[2,3],[3,4],[0,5],[1,6],[2,7],[3,8]]
+
+**Output:** 6
+
+**Explanation:**
+
+![](https://assets.leetcode.com/uploads/2024/06/03/screenshot-2024-06-03-193552.png)
+
+There are 6 good nodes in the given tree. They are colored in the image above.
+
+**Example 3:**
+
+**Input:** edges = [[0,1],[1,2],[1,3],[1,4],[0,5],[5,6],[6,7],[7,8],[0,9],[9,10],[9,12],[10,11]]
+
+**Output:** 12
+
+**Explanation:**
+
+![](https://assets.leetcode.com/uploads/2024/08/08/rob.jpg)
+
+All nodes except node 9 are good.
+
+**Constraints:**
+
+*   <code>2 <= n <= 10<sup>5</sup></code>
+*   `edges.length == n - 1`
+*   `edges[i].length == 2`
+*   <code>0 <= a<sub>i</sub>, b<sub>i</sub> < n</code>
+*   The input is generated such that `edges` represents a valid tree.

src/main/kotlin/g3201_3300/s3250_find_the_count_of_monotonic_pairs_i/Solution.kt

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+package g3201_3300.s3250_find_the_count_of_monotonic_pairs_i
+
+// #Hard #Array #Dynamic_Programming #Math #Prefix_Sum #Combinatorics
+// #2024_08_13_Time_241_ms_(100.00%)_Space_39.2_MB_(100.00%)
+
+import kotlin.math.max
+import kotlin.math.min
+
+class Solution {
+    fun countOfPairs(nums: IntArray): Int {
+        val maxShift = IntArray(nums.size)
+        maxShift[0] = nums[0]
+        var currShift = 0
+        for (i in 1 until nums.size) {
+            currShift = max(currShift, (nums[i] - maxShift[i - 1]))
+            maxShift[i] = min(maxShift[i - 1], (nums[i] - currShift))
+            if (maxShift[i] < 0) {
+                return 0
+            }
+        }
+        val cases = getAllCases(nums, maxShift)
+        return cases[nums.size - 1]!![maxShift[nums.size - 1]]
+    }
+
+    private fun getAllCases(nums: IntArray, maxShift: IntArray): Array<IntArray?> {
+        var currCases: IntArray
+        val cases = arrayOfNulls<IntArray>(nums.size)
+        cases[0] = IntArray(maxShift[0] + 1)
+        for (i in cases[0]!!.indices) {
+            cases[0]!![i] = i + 1
+        }
+        for (i in 1 until nums.size) {
+            currCases = IntArray(maxShift[i] + 1)
+            currCases[0] = 1
+            for (j in 1 until currCases.size) {
+                val prevCases =
+                    if (j < cases[i - 1]!!.size
+                    ) cases[i - 1]!![j]
+                    else cases[i - 1]!![cases[i - 1]!!.size - 1]
+                currCases[j] = (currCases[j - 1] + prevCases) % (1000000000 + 7)
+            }
+            cases[i] = currCases
+        }
+        return cases
+    }
+}

src/main/kotlin/g3201_3300/s3250_find_the_count_of_monotonic_pairs_i/readme.md

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+3250\. Find the Count of Monotonic Pairs I
+
+Hard
+
+You are given an array of **positive** integers `nums` of length `n`.
+
+We call a pair of **non-negative** integer arrays `(arr1, arr2)` **monotonic** if:
+
+*   The lengths of both arrays are `n`.
+*   `arr1` is monotonically **non-decreasing**, in other words, `arr1[0] <= arr1[1] <= ... <= arr1[n - 1]`.
+*   `arr2` is monotonically **non-increasing**, in other words, `arr2[0] >= arr2[1] >= ... >= arr2[n - 1]`.
+*   `arr1[i] + arr2[i] == nums[i]` for all `0 <= i <= n - 1`.
+
+Return the count of **monotonic** pairs.
+
+Since the answer may be very large, return it **modulo** <code>10<sup>9</sup> + 7</code>.
+
+**Example 1:**
+
+**Input:** nums = [2,3,2]
+
+**Output:** 4
+
+**Explanation:**
+
+The good pairs are:
+
+1.  `([0, 1, 1], [2, 2, 1])`
+2.  `([0, 1, 2], [2, 2, 0])`
+3.  `([0, 2, 2], [2, 1, 0])`
+4.  `([1, 2, 2], [1, 1, 0])`
+
+**Example 2:**
+
+**Input:** nums = [5,5,5,5]
+
+**Output:** 126
+
+**Constraints:**
+
+*   `1 <= n == nums.length <= 2000`
+*   `1 <= nums[i] <= 50`

src/main/kotlin/g3201_3300/s3251_find_the_count_of_monotonic_pairs_ii/Solution.kt

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+package g3201_3300.s3251_find_the_count_of_monotonic_pairs_ii
+
+// #Hard #Array #Dynamic_Programming #Math #Prefix_Sum #Combinatorics
+// #2024_08_13_Time_291_ms_(100.00%)_Space_47_MB_(100.00%)
+
+import kotlin.math.max
+
+class Solution {
+    fun countOfPairs(nums: IntArray): Int {
+        var prefixZeros = 0
+        val n = nums.size
+        // Calculate prefix zeros
+        for (i in 1 until n) {
+            prefixZeros += max((nums[i] - nums[i - 1]), 0)
+        }
+        val row = n + 1
+        val col = nums[n - 1] + 1 - prefixZeros
+        if (col <= 0) {
+            return 0
+        }
+        // Initialize dp array
+        val dp = IntArray(col)
+        dp.fill(1)
+        // Fill dp array
+        for (r in 1 until row) {
+            for (c in 1 until col) {
+                dp[c] = (dp[c] + dp[c - 1]) % MOD
+            }
+        }
+        return dp[col - 1]
+    }
+
+    companion object {
+        private const val MOD = 1000000007
+    }
+}

src/main/kotlin/g3201_3300/s3251_find_the_count_of_monotonic_pairs_ii/readme.md

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+3251\. Find the Count of Monotonic Pairs II
+
+Hard
+
+You are given an array of **positive** integers `nums` of length `n`.
+
+We call a pair of **non-negative** integer arrays `(arr1, arr2)` **monotonic** if:
+
+*   The lengths of both arrays are `n`.
+*   `arr1` is monotonically **non-decreasing**, in other words, `arr1[0] <= arr1[1] <= ... <= arr1[n - 1]`.
+*   `arr2` is monotonically **non-increasing**, in other words, `arr2[0] >= arr2[1] >= ... >= arr2[n - 1]`.
+*   `arr1[i] + arr2[i] == nums[i]` for all `0 <= i <= n - 1`.
+
+Return the count of **monotonic** pairs.
+
+Since the answer may be very large, return it **modulo** <code>10<sup>9</sup> + 7</code>.
+
+**Example 1:**
+
+**Input:** nums = [2,3,2]
+
+**Output:** 4
+
+**Explanation:**
+
+The good pairs are:
+
+1.  `([0, 1, 1], [2, 2, 1])`
+2.  `([0, 1, 2], [2, 2, 0])`
+3.  `([0, 2, 2], [2, 1, 0])`
+4.  `([1, 2, 2], [1, 1, 0])`
+
+**Example 2:**
+
+**Input:** nums = [5,5,5,5]
+
+**Output:** 126
+
+**Constraints:**
+
+*   `1 <= n == nums.length <= 2000`
+*   `1 <= nums[i] <= 1000`