Create count-the-number-of-incremovable-subarrays-i.cpp

Author: kamyu104

C++/count-the-number-of-incremovable-subarrays-i.cpp

@@ -0,0 +1,67 @@
+// Time:  O(n)
+// Space: O(1)
+
+// two pointers
+class Solution {
+public:
+    long long incremovableSubarrayCount(vector<int>& nums) {
+        int j = size(nums) - 1;
+        for (; j >= 1; --j) {
+            if (!(nums[j - 1] < nums[j])) {
+                break;
+            }
+        }
+        if (j == 0) {
+            return (size(nums) + 1) * size(nums) / 2;
+        }
+        int64_t result = size(nums) - j + 1;
+        for (int i = 0; i + 1 < size(nums); ++i) {
+            while (j < size(nums) && !(nums[i] < nums[j])) {
+                ++j;
+            }
+            result += size(nums) - j + 1;
+            if (!(nums[i] < nums[i + 1])) {
+                break;
+            }
+        }
+        return result;
+    }
+};
+
+// Time:  O(n^3)
+// Space: O(1)
+// brute force
+class Solution2 {
+public:
+    long long incremovableSubarrayCount(vector<int>& nums) {
+        int64_t result = 0;
+        for (int left = 0; left < size(nums); ++left) {
+            for (int right = left; right < size(nums); ++right) {
+                bool check = left == 0 || right == size(nums) - 1 || nums[left - 1] < nums[right + 1];
+                if (!check) {
+                    continue;
+                }
+                for (int i = 0; i + 1 < left; ++i) {
+                    if (!(nums[i] < nums[i + 1])) {
+                        check = false;
+                        break;
+                    }
+                }
+                if (!check) {
+                    continue;
+                }
+                for (int i = right + 1; i + 1 < size(nums); ++i) {
+                    if (!(nums[i] < nums[i + 1])) {
+                        check = false;
+                        break;
+                    }
+                }
+                if (!check) {
+                    continue;
+                }
+                ++result;
+            }
+        }
+        return result;
+    }
+};