# Maximum length of Strictly Increasing Sub-array after removing at most one element

Given an array arr[], the task is to remove at most one element and calculate the maximum length of strictly increasing subarray.

Examples:

Input: arr[] = {1, 2, 5, 3, 4}
Output: 4
After deleting 5, the resulting array will be {1, 2, 3, 4}
and the maximum length of its strictly increasing subarray is 4.

Input: arr[] = {1, 2}
Output: 2
The complete array is already strictly increasing.

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

• Create two arrays pre[] and pos[] of size N.
• Iterate over the input array arr[] from (0, N) to find out the contribution of the current element arr[i] in the array till now [0, i) and update the pre[] array if it contributes in the strictly increasing subarray.
• Iterate over the input array arr[] from [N – 2, 0] to find out the contribution of the current element arr[j] in the array till now (N, j) and update the pos[] array if arr[j] contributes in the longest increasing subarray.
• Calculate the maximum length of the stricly increasing subarray without removing any element.
• Iterate over the array pre[] and pos[] to find out the contribution of the current element by excluding that element.
• Maintain a variable ans to find the maximum found till now.

Below is the implementation of the above approach:

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function to return the maximum length of ` `// strictly increasing subarray after ` `// removing atmost one element ` `int` `maxIncSubarr(``int` `a[], ``int` `n) ` `{ ` `    ``// Create two arrays pre and pos ` `    ``int` `pre[n] = { 0 }; ` `    ``int` `pos[n] = { 0 }; ` `    ``pre = 1; ` `    ``pos[n - 1] = 1; ` `    ``int` `l = 0; ` ` `  `    ``// Find out the contribution of the current ` `    ``// element in array[0, i] and update pre[i] ` `    ``for` `(``int` `i = 1; i < n; i++) { ` `        ``if` `(a[i] > a[i - 1]) ` `            ``pre[i] = pre[i - 1] + 1; ` `        ``else` `            ``pre[i] = 1; ` `    ``} ` ` `  `    ``// Find out the contribution of the current ` `    ``// element in array[N - 1, i] and update pos[i] ` `    ``l = 1; ` `    ``for` `(``int` `i = n - 2; i >= 0; i--) { ` `        ``if` `(a[i] < a[i + 1]) ` `            ``pos[i] = pos[i + 1] + 1; ` `        ``else` `            ``pos[i] = 1; ` `    ``} ` ` `  `    ``// Calculate the maximum length of the ` `    ``// stricly increasing subarray without ` `    ``// removing any element ` `    ``int` `ans = 0; ` `    ``l = 1; ` `    ``for` `(``int` `i = 1; i < n; i++) { ` `        ``if` `(a[i] > a[i - 1]) ` `            ``l++; ` `        ``else` `            ``l = 1; ` `        ``ans = max(ans, l); ` `    ``} ` ` `  `    ``// Calculate the maximum length of the ` `    ``// strictly increasing subarray after ` `    ``// removing the current element ` `    ``for` `(``int` `i = 1; i <= n - 2; i++) { ` `        ``if` `(a[i - 1] < a[i + 1]) ` `            ``ans = max(pre[i - 1] + pos[i + 1], ans); ` `    ``} ` ` `  `    ``return` `ans; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 1, 2 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(``int``); ` ` `  `    ``cout << maxIncSubarr(arr, n); ` ` `  `    ``return` `0; ` `} `

 `// Java implementation of the approach  ` `class` `GFG  ` `{ ` `     `  `    ``// Function to return the maximum length of  ` `    ``// strictly increasing subarray after  ` `    ``// removing atmost one element  ` `    ``static` `int` `maxIncSubarr(``int` `a[], ``int` `n)  ` `    ``{  ` `        ``// Create two arrays pre and pos  ` `        ``int` `pre[] = ``new` `int``[n] ;  ` `        ``int` `pos[] = ``new` `int``[n] ;  ` `        ``pre[``0``] = ``1``;  ` `        ``pos[n - ``1``] = ``1``;  ` `        ``int` `l = ``0``;  ` `     `  `        ``// Find out the contribution of the current  ` `        ``// element in array[0, i] and update pre[i]  ` `        ``for` `(``int` `i = ``1``; i < n; i++) ` `        ``{  ` `            ``if` `(a[i] > a[i - ``1``])  ` `                ``pre[i] = pre[i - ``1``] + ``1``;  ` `            ``else` `                ``pre[i] = ``1``;  ` `        ``}  ` `     `  `        ``// Find out the contribution of the current  ` `        ``// element in array[N - 1, i] and update pos[i]  ` `        ``l = ``1``;  ` `        ``for` `(``int` `i = n - ``2``; i >= ``0``; i--) ` `        ``{  ` `            ``if` `(a[i] < a[i + ``1``])  ` `                ``pos[i] = pos[i + ``1``] + ``1``;  ` `            ``else` `                ``pos[i] = ``1``;  ` `        ``}  ` `     `  `        ``// Calculate the maximum length of the  ` `        ``// stricly increasing subarray without  ` `        ``// removing any element  ` `        ``int` `ans = ``0``;  ` `        ``l = ``1``;  ` `        ``for` `(``int` `i = ``1``; i < n; i++) ` `        ``{  ` `            ``if` `(a[i] > a[i - ``1``])  ` `                ``l++;  ` `            ``else` `                ``l = ``1``;  ` `            ``ans = Math.max(ans, l);  ` `        ``}  ` `     `  `        ``// Calculate the maximum length of the  ` `        ``// strictly increasing subarray after  ` `        ``// removing the current element  ` `        ``for` `(``int` `i = ``1``; i <= n - ``2``; i++)  ` `        ``{  ` `            ``if` `(a[i - ``1``] < a[i + ``1``])  ` `                ``ans = Math.max(pre[i - ``1``] +  ` `                                ``pos[i + ``1``], ans);  ` `        ``}  ` `        ``return` `ans;  ` `    ``}  ` `     `  `    ``// Driver code  ` `    ``public` `static` `void` `main (String[] args) ` `    ``{  ` `        ``int` `arr[] = {``1``, ``2``};  ` `        ``int` `n = arr.length;  ` `     `  `        ``System.out.println(maxIncSubarr(arr, n));  ` `    ``}  ` `} ` ` `  `// This code is contributed by AnkitRai01 `

 `# Python implementation of the approach  ` ` `  `# Function to return the maximum length of ` `# strictly increasing subarray after ` `# removing atmost one element ` `def` `maxIncSubarr(a, n): ` `     `  `    ``# Create two arrays pre and pos ` `    ``pre ``=` `[``0``] ``*` `n; ` `    ``pos ``=` `[``0``] ``*` `n; ` `    ``pre[``0``] ``=` `1``; ` `    ``pos[n ``-` `1``] ``=` `1``; ` `    ``l ``=` `0``; ` ` `  `    ``# Find out the contribution of the current ` `    ``# element in array[0, i] and update pre[i] ` `    ``for` `i ``in` `range``(``1``, n): ` `        ``if` `(a[i] > a[i ``-` `1``]): ` `            ``pre[i] ``=` `pre[i ``-` `1``] ``+` `1``; ` `        ``else``: ` `            ``pre[i] ``=` `1``; ` `     `  `    ``# Find out the contribution of the current ` `    ``# element in array[N - 1, i] and update pos[i] ` `    ``l ``=` `1``; ` `    ``for` `i ``in` `range``(n ``-` `2``, ``-``1``, ``-``1``): ` `        ``if` `(a[i] < a[i ``+` `1``]): ` `            ``pos[i] ``=` `pos[i ``+` `1``] ``+` `1``; ` `        ``else``: ` `            ``pos[i] ``=` `1``; ` `     `  `    ``# Calculate the maximum length of the ` `    ``# stricly increasing subarray without ` `    ``# removing any element ` `    ``ans ``=` `0``; ` `    ``l ``=` `1``; ` `    ``for` `i ``in` `range``(``1``, n): ` `        ``if` `(a[i] > a[i ``-` `1``]): ` `            ``l ``+``=` `1``; ` `        ``else``: ` `            ``l ``=` `1``; ` `        ``ans ``=` `max``(ans, l); ` `     `  `    ``# Calculate the maximum length of the ` `    ``# strictly increasing subarray after ` `    ``# removing the current element ` `    ``for` `i ``in` `range``(``1``, n ``-` `2``): ` `        ``if` `(a[i ``-` `1``] < a[i ``+` `1``]): ` `            ``ans ``=` `max``(pre[i ``-` `1``] ``+` `pos[i ``+` `1``], ans); ` `     `  `    ``return` `ans; ` ` `  `# Driver code ` `if` `__name__ ``=``=` `'__main__'``: ` `    ``arr ``=` `[ ``1``, ``2` `]; ` `    ``n ``=` `len``(arr); ` ` `  `    ``print``(maxIncSubarr(arr, n)); ` `     `  `# This code is contributed by PrinciRaj1992 `

 `// C# implementation of the approach  ` `using` `System; ` ` `  `class` `GFG  ` `{ ` `     `  `    ``// Function to return the maximum length of  ` `    ``// strictly increasing subarray after  ` `    ``// removing atmost one element  ` `    ``static` `int` `maxIncSubarr(``int` `[]a, ``int` `n)  ` `    ``{  ` `        ``// Create two arrays pre and pos  ` `        ``int` `[]pre = ``new` `int``[n] ;  ` `        ``int` `[]pos = ``new` `int``[n] ;  ` `        ``pre = 1;  ` `        ``pos[n - 1] = 1;  ` `        ``int` `l = 0;  ` `     `  `        ``// Find out the contribution of the current  ` `        ``// element in array[0, i] and update pre[i]  ` `        ``for` `(``int` `i = 1; i < n; i++) ` `        ``{  ` `            ``if` `(a[i] > a[i - 1])  ` `                ``pre[i] = pre[i - 1] + 1;  ` `            ``else` `                ``pre[i] = 1;  ` `        ``}  ` `     `  `        ``// Find out the contribution of the current  ` `        ``// element in array[N - 1, i] and update pos[i]  ` `        ``l = 1;  ` `        ``for` `(``int` `i = n - 2; i >= 0; i--) ` `        ``{  ` `            ``if` `(a[i] < a[i + 1])  ` `                ``pos[i] = pos[i + 1] + 1;  ` `            ``else` `                ``pos[i] = 1;  ` `        ``}  ` `     `  `        ``// Calculate the maximum length of the  ` `        ``// stricly increasing subarray without  ` `        ``// removing any element  ` `        ``int` `ans = 0;  ` `        ``l = 1;  ` `        ``for` `(``int` `i = 1; i < n; i++) ` `        ``{  ` `            ``if` `(a[i] > a[i - 1])  ` `                ``l++;  ` `            ``else` `                ``l = 1;  ` `            ``ans = Math.Max(ans, l);  ` `        ``}  ` `     `  `        ``// Calculate the maximum length of the  ` `        ``// strictly increasing subarray after  ` `        ``// removing the current element  ` `        ``for` `(``int` `i = 1; i <= n - 2; i++)  ` `        ``{  ` `            ``if` `(a[i - 1] < a[i + 1])  ` `                ``ans = Math.Max(pre[i - 1] +  ` `                                ``pos[i + 1], ans);  ` `        ``}  ` `        ``return` `ans;  ` `    ``}  ` `     `  `    ``// Driver code  ` `    ``public` `static` `void` `Main() ` `    ``{  ` `        ``int` `[]arr = {1, 2};  ` `        ``int` `n = arr.Length;  ` `     `  `        ``Console.WriteLine(maxIncSubarr(arr, n));  ` `    ``}  ` `} ` ` `  `// This code is contributed by AnkitRai01 `

Output:
```2
```

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