2972. Count the Number of Incremovable Subarrays II

Author: sergeyleschev

2501-3000/2972. Count the Number of Incremovable Subarrays II.swift

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+class Solution {
+
+    // Solution by Sergey Leschev
+    // 2972. Count the Number of Incremovable Subarrays II
+
+    // Two pointer
+    // O(N)
+
+    func countSortedArrays(_ arr1: [Int], _ arr2: [Int]) -> Int {
+        let n1 = arr1.count
+        let n2 = arr2.count
+
+        var result = 0
+        var i = 0
+        var j = 0
+
+        while i < n1 && j < n2 {
+            if arr1[i] < arr2[j] {
+                result += (n2 - j)
+                i += 1
+            } else {
+                j += 1
+            }
+        }
+
+        return result
+    }
+
+    func incremovableSubarrayCount(_ nums: [Int]) -> Int {
+        let n = nums.count
+
+        if n == 1 {
+            return 1
+        }
+
+        var i = 0
+        var j = n - 1
+        var arr1: [Int] = []
+        var arr2: [Int] = []
+
+        while (i + 1) < n && nums[i] < nums[i + 1] {
+            arr1.append(nums[i])
+            i += 1
+        }
+        arr1.append(nums[i])
+
+        while (j - 1) >= 0 && nums[j] > nums[j - 1] {
+            arr2.append(nums[j])
+            j -= 1
+        }
+        arr2.append(nums[j])
+        arr2.reverse()
+
+        if j < i {
+            let ans = n * (n + 1) / 2
+            return ans
+        }
+
+        var ans = 0
+        ans += arr1.count  // 1
+        ans += arr2.count  // 2
+        ans += countSortedArrays(arr1, arr2)  // 3
+        ans += 1  // 4
+
+        return ans
+    }
+}