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Longest sequence of positive integers in an array
• Difficulty Level : Easy
• Last Updated : 29 May, 2018

Find the longest running positive sequence in an array.

Examples:

```Input : arr[] = {1, 2, -3, 2, 3, 4, -6, 1,
2, 3, 4, 5, -8, 5, 6}
Output :Index : 7, length : 5

Input : arr[] = {-3, -6, -1, -3, -8}
Output : No positive sequence detected.
```

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

A simple solution is to use two nested loops. In the outer loop, we look for positive elements. In the inner loop, we count number of positives starting with the positive element picked by outer loop. Time complexity of this solution is O(n^2).

An efficient solution is to use one single loop. We keep incrementing count while we see positive integers. We reset count to 0 after seeing a negative. Before resetting, we check if count is more than maximum.

## C++

 `// CPP program to find longest running sequence``// of positive integers.``#include ``using` `namespace` `std;`` ` `// Prints longest sequence of positive integers in``// an array.``void` `getLongestSeq(``int` `a[], ``int` `n)``{``    ``// Variables to keep track of maximum length and ``    ``// starting point of maximum length. And same ``    ``// for current length.``    ``int` `maxIdx = 0, maxLen = 0, currLen = 0, currIdx = 0;`` ` `    ``for` `(``int` `k = 0; k < n; k++) {``        ``if` `(a[k] > 0) {``            ``currLen++;`` ` `            ``// New sequence, store``            ``// beginning index.``            ``if` `(currLen == 1) ``                ``currIdx = k;            ``        ``}``        ``else` `{``            ``if` `(currLen > maxLen) {``                ``maxLen = currLen;``                ``maxIdx = currIdx;``            ``}``            ``currLen  = 0;``        ``}``    ``}`` ` `    ``if` `(maxLen > 0) ``        ``cout << ``"Length "` `<< maxLen ``             ``<< ``", starting index "` `<< maxIdx << endl;    ``    ``else` `        ``cout << ``"No positive sequence detected."` `<< endl;``     ` `    ``return``;``}`` ` `// Driver code``int` `main()``{``    ``int` `arr[] = { 1, 2, -3, 2, 3, 4, -6, ``               ``1, 2, 3, 4, 5, -8, 5, 6 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(``int``);``    ``getLongestSeq(arr, n);``    ``return` `0;``}`

## Java

 `// Java program to find longest running ``// sequence of positive integers``import` `java.io.*;`` ` `class` `GFG {``     ` `    ``// Prints longest sequence of ``    ``// positive integers in an array.``    ``static` `void` `getLongestSeq(``int` `a[], ``int` `n)``    ``{``        ``// Variables to keep track of maximum``        ``// length and  starting point of ``        ``// maximum length. And same for current``        ``// length.``        ``int` `maxIdx = ``0``, maxLen = ``0``, currLen = ``0``, currIdx = ``0``;``     ` `        ``for` `(``int` `k = ``0``; k < n; k++) ``        ``{``            ``if` `(a[k] > ``0``)``            ``{``                ``currLen++;``     ` `                ``// New sequence, store``                ``// beginning index.``                ``if` `(currLen == ``1``) ``                    ``currIdx = k;         ``            ``}``            ``else``            ``{``                ``if` `(currLen > maxLen) ``                ``{``                    ``maxLen = currLen;``                    ``maxIdx = currIdx;``                ``}``                ``currLen = ``0``;``            ``}``        ``}``     ` `        ``if` `(maxLen > ``0``) ``        ``{``            ``System.out.print( ``"Length "` `+ maxLen) ; ``            ``System.out.print( ``",starting index "` `+ maxIdx );``        ``}``        ``else``            ``System.out.println(``"No positive sequence detected."``) ;``         ` `        ``return``;``    ``}``     ` `    ``// Driver code``    ``public` `static` `void` `main (String[] args) ``    ``{``        ``int` `arr[] = { ``1``, ``2``, -``3``, ``2``, ``3``, ``4``, -``6``, ``                      ``1``, ``2``, ``3``, ``4``, ``5``, -``8``, ``5``, ``6` `};``        ``int` `n = arr.length;``        ``getLongestSeq(arr, n);``     ` `    ``}``}`` ` `// This article is contributed by vt_m.`

## Python3

 `# Python code to find longest running ``# sequence of positive integers.`` ` `def` `getLongestSeq(a, n):``    ``maxIdx ``=` `0``    ``maxLen ``=` `0``    ``currLen ``=` `0``    ``currIdx ``=` `0``    ``for` `k ``in` `range``(n):``        ``if` `a[k] > ``0``:``            ``currLen ``+``=``1`` ` `            ``# New sequence, store``            ``# beginning index.``            ``if` `currLen ``=``=` `1``:``                ``currIdx ``=` `k``        ``else``:``            ``if` `currLen > maxLen:``                ``maxLen ``=` `currLen``                ``maxIdx ``=` `currIdx``            ``currLen ``=` `0``             ` `    ``if` `maxLen > ``0``:``        ``print``(``'Index : '``,maxIdx,``',Length : '``,maxLen,)``    ``else``:``        ``print``(``"No positive sequence detected."``)`` ` `# Driver code``arr ``=` `[ ``1``, ``2``, ``-``3``, ``2``, ``3``, ``4``, ``-``6``, ``        ``1``, ``2``, ``3``, ``4``, ``5``, ``-``8``, ``5``, ``6``] ``n ``=` `len``(arr)``getLongestSeq(arr, n)`` ` `# This code is contributed by "Abhishek Sharma 44"`

## C#

 `// C# program to find longest running``// sequence of positive integers.``using` `System;`` ` `class` `GFG {``     ` `    ``// Prints longest sequence of ``    ``// positive integers in an array.``    ``static` `void` `getLongestSeq(``int` `[]a, ``int` `n)``    ``{``         ` `        ``// Variables to keep track of maximum``        ``// length and starting point of ``        ``// maximum length. And same for current``        ``// length.``        ``int` `maxIdx = 0, maxLen = 0, currLen = 0,``            ``currIdx = 0;``     ` `        ``for` `(``int` `k = 0; k < n; k++) ``        ``{``            ``if` `(a[k] > 0)``            ``{``                ``currLen++;``     ` `                ``// New sequence, store``                ``// beginning index.``                ``if` `(currLen == 1) ``                    ``currIdx = k;         ``            ``}``            ``else``            ``{``                ``if` `(currLen > maxLen) ``                ``{``                    ``maxLen = currLen;``                    ``maxIdx = currIdx;``                ``}``                ``currLen = 0;``            ``}``        ``}``     ` `        ``if` `(maxLen > 0) ``        ``{``            ``Console.Write( ``"Length "` `+ maxLen) ; ``            ``Console.WriteLine( ``",starting index "``                                      ``+ maxIdx );``        ``}``        ``else``            ``Console.WriteLine(``"No positive sequence"``                                   ``+ ``" detected."``) ;``         ` `        ``return``;``    ``}``     ` `    ``// driver code``    ``public` `static` `void` `Main()``    ``{``        ``int` `[]arr = { 1, 2, -3, 2, 3, 4, -6, ``                    ``1, 2, 3, 4, 5, -8, 5, 6 };``        ``int` `n = arr.Length;``        ``getLongestSeq(arr, n);``         ` `    ``} `` ` `}``// This code is contributed by Sam007`

## PHP

 ` 0) {``            ``\$currLen``++;`` ` `            ``// New sequence, store``            ``// beginning index.``            ``if` `(``\$currLen` `== 1) ``                ``\$currIdx` `= ``\$k``;         ``        ``}``        ``else` `{``            ``if` `(``\$currLen` `> ``\$maxLen``) {``                ``\$maxLen` `= ``\$currLen``;``                ``\$maxIdx` `= ``\$currIdx``;``            ``}``            ``\$currLen` `= 0;``        ``}``    ``}`` ` `    ``if` `(``\$maxLen` `> 0) ``        ``echo` `"Length "` `. ``\$maxLen``. ``             ``", starting index "` `. ``             ``\$maxIdx` `.``"\n"` `; ``    ``else``        ``echo` `"No positive sequence detected."``.``"\n"``;``     ` `    ``return``;``}`` ` `    ``// Driver Code``    ``\$arr` `= ``array``(1, 2, -3, 2, 3, 4, -6, ``                 ``1, 2, 3, 4, 5, -8, 5, 6);``    ``\$n` `= ``count``(``\$arr``);``    ``getLongestSeq(``\$arr``, ``\$n``);``     ` `// This code is contributed by Sam007``?>`

Output:
```Length 5, starting index 7
```

The algorithm is O(n) time and O(1) auxiliary space.

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