# Count of sub-arrays with odd product

Given an integer array **arr[]** of size **N**, the task is to count the number of sub-arrays that have an odd product.**Examples:**

Input :arr[] = {5, 1, 2, 3, 4}Output :4Explanation:The sub-arrays with odd product are-

{5}, {1}, {3}, {5, 1}. Hence the count is 4.Input :arr[] = {12, 15, 7, 3, 25, 6, 2, 1, 1, 7}Output :16

**Naive Approach:** A simple solution is to calculate the product of every sub-array and check whether it is odd or not and calculate the count accordingly. **Time Complexity:** *O(N ^{2})*

**Efficient Approach:**An odd product is possible only by the product of odd numbers. Thus, for every

**K**continuous odd numbers in the array, the count of sub-arrays with the odd product increases by

**K*(K+1)/2**. One way of counting continuous odd numbers is to calculate the difference between the indexes of every two consecutive even numbers and subtract it by

**1**. For the calculation,

**-1**and

**N**are considered as indexes of even numbers.

Below is the implementation of the above approach:

## C++

`// C++ program to find the count of` `// sub-arrays with odd product` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function that returns the count of` `// sub-arrays with odd product` `int` `countSubArrayWithOddProduct(` `int` `* A, ` `int` `N)` `{` ` ` `// Initialize the count variable` ` ` `int` `count = 0;` ` ` `// Initialize variable to store the` ` ` `// last index with even number` ` ` `int` `last = -1;` ` ` `// Initialize variable to store` ` ` `// count of continuous odd numbers` ` ` `int` `K = 0;` ` ` `// Loop through the array` ` ` `for` `(` `int` `i = 0; i < N; i++) {` ` ` `// Check if the number` ` ` `// is even or not` ` ` `if` `(A[i] % 2 == 0) {` ` ` `// Calculate count of continuous` ` ` `// odd numbers` ` ` `K = (i - last - 1);` ` ` `// Increase the count of sub-arrays` ` ` `// with odd product` ` ` `count += (K * (K + 1) / 2);` ` ` `// Store the index of last` ` ` `// even number` ` ` `last = i;` ` ` `}` ` ` `}` ` ` `// N considered as index of` ` ` `// even number` ` ` `K = (N - last - 1);` ` ` `count += (K * (K + 1) / 2);` ` ` `return` `count;` `}` `// Driver Code` `int` `main()` `{` ` ` `int` `arr[] = { 12, 15, 7, 3, 25,` ` ` `6, 2, 1, 1, 7 };` ` ` `int` `n = ` `sizeof` `(arr) / ` `sizeof` `(arr[0]);` ` ` `// Function call` ` ` `cout << countSubArrayWithOddProduct(arr, n);` ` ` `return` `0;` `}` |

## Java

`// Java program to find the count of` `// sub-arrays with odd product` `class` `GFG {` `// Function that returns the count of` `// sub-arrays with odd product` `static` `int` `countSubArrayWithOddProduct(` `int` `A[],` ` ` `int` `N)` `{` ` ` ` ` `// Initialize the count variable` ` ` `int` `count = ` `0` `;` ` ` `// Initialize variable to store the` ` ` `// last index with even number` ` ` `int` `last = -` `1` `;` ` ` `// Initialize variable to store` ` ` `// count of continuous odd numbers` ` ` `int` `K = ` `0` `;` ` ` `// Loop through the array` ` ` `for` `(` `int` `i = ` `0` `; i < N; i++)` ` ` `{` ` ` `// Check if the number` ` ` `// is even or not` ` ` `if` `(A[i] % ` `2` `== ` `0` `)` ` ` `{` ` ` `// Calculate count of continuous` ` ` `// odd numbers` ` ` `K = (i - last - ` `1` `);` ` ` ` ` `// Increase the count of sub-arrays` ` ` `// with odd product` ` ` `count += (K * (K + ` `1` `) / ` `2` `);` ` ` ` ` `// Store the index of last` ` ` `// even number` ` ` `last = i;` ` ` `}` ` ` `}` ` ` `// N considered as index of` ` ` `// even number` ` ` `K = (N - last - ` `1` `);` ` ` `count += (K * (K + ` `1` `) / ` `2` `);` ` ` ` ` `return` `count;` `}` `// Driver Code` `public` `static` `void` `main(String args[])` `{` ` ` `int` `arr[] = { ` `12` `, ` `15` `, ` `7` `, ` `3` `, ` `25` `, ` `6` `, ` `2` `, ` `1` `, ` `1` `, ` `7` `};` ` ` `int` `n = arr.length;` ` ` `// Function call` ` ` `System.out.println(countSubArrayWithOddProduct(arr, n));` `}` `}` `// This code is contributed by rutvik_56` |

## Python3

`# Python3 program to find the count of` `# sub-arrays with odd product` `# Function that returns the count of` `# sub-arrays with odd product` `def` `countSubArrayWithOddProduct(A, N):` ` ` ` ` `# Initialize the count variable` ` ` `count ` `=` `0` ` ` `# Initialize variable to store the` ` ` `# last index with even number` ` ` `last ` `=` `-` `1` ` ` `# Initialize variable to store` ` ` `# count of continuous odd numbers` ` ` `K ` `=` `0` ` ` `# Loop through the array` ` ` `for` `i ` `in` `range` `(N):` ` ` ` ` `# Check if the number` ` ` `# is even or not` ` ` `if` `(A[i] ` `%` `2` `=` `=` `0` `):` ` ` ` ` `# Calculate count of continuous` ` ` `# odd numbers` ` ` `K ` `=` `(i ` `-` `last ` `-` `1` `)` ` ` `# Increase the count of sub-arrays` ` ` `# with odd product` ` ` `count ` `+` `=` `(K ` `*` `(K ` `+` `1` `) ` `/` `2` `)` ` ` `# Store the index of last` ` ` `# even number` ` ` `last ` `=` `i` ` ` `# N considered as index of` ` ` `# even number` ` ` `K ` `=` `(N ` `-` `last ` `-` `1` `)` ` ` `count ` `+` `=` `(K ` `*` `(K ` `+` `1` `) ` `/` `2` `)` ` ` `return` `count` `# Driver Code` `if` `__name__ ` `=` `=` `'__main__'` `:` ` ` ` ` `arr ` `=` `[ ` `12` `, ` `15` `, ` `7` `, ` `3` `, ` `25` `, ` `6` `, ` `2` `, ` `1` `, ` `1` `, ` `7` `]` ` ` `n ` `=` `len` `(arr)` ` ` `# Function call` ` ` `print` `(` `int` `(countSubArrayWithOddProduct(arr, n)))` `# This code is contributed by Bhupendra_Singh` |

## C#

`// C# program to find the count of` `// sub-arrays with odd product` `using` `System;` `class` `GFG{` `// Function that returns the count of` `// sub-arrays with odd product ` `static` `int` `countSubArrayWithOddProduct(` `int` `[] A,` ` ` `int` `N)` `{` ` ` ` ` `// Initialize the count variable` ` ` `int` `count = 0;` ` ` ` ` `// Initialize variable to store the` ` ` `// last index with even number` ` ` `int` `last = -1;` ` ` ` ` `// Initialize variable to store` ` ` `// count of continuous odd numbers` ` ` `int` `K = 0;` ` ` ` ` `// Loop through the array` ` ` `for` `(` `int` `i = 0; i < N; i++)` ` ` `{` ` ` ` ` `// Check if the number` ` ` `// is even or not` ` ` `if` `(A[i] % 2 == 0)` ` ` `{` ` ` ` ` `// Calculate count of continuous` ` ` `// odd numbers` ` ` `K = (i - last - 1);` ` ` ` ` `// Increase the count of sub-arrays` ` ` `// with odd product` ` ` `count += (K * (K + 1) / 2);` ` ` ` ` `// Store the index of last` ` ` `// even number` ` ` `last = i;` ` ` `}` ` ` `}` ` ` ` ` `// N considered as index of` ` ` `// even number` ` ` `K = (N - last - 1);` ` ` `count += (K * (K + 1) / 2);` ` ` ` ` `return` `count;` `}` `// Driver code` `static` `void` `Main()` `{` ` ` `int` `[] arr = { 12, 15, 7, 3, 25,` ` ` `6, 2, 1, 1, 7 };` ` ` `int` `n = arr.Length;` ` ` ` ` `// Function call` ` ` `Console.WriteLine(countSubArrayWithOddProduct(arr, n));` `}` `}` `// This code is contributed by divyeshrabadiya07` |

## Javascript

`<script>` `// Javascript program to find the count of` `// sub-arrays with odd product` `// Function that returns the count of` `// sub-arrays with odd product` `function` `countSubArrayWithOddProduct(A, N)` `{` ` ` `// Initialize the count variable` ` ` `var` `count = 0;` ` ` `// Initialize variable to store the` ` ` `// last index with even number` ` ` `var` `last = -1;` ` ` `// Initialize variable to store` ` ` `// count of continuous odd numbers` ` ` `var` `K = 0;` ` ` `// Loop through the array` ` ` `for` `(` `var` `i = 0; i < N; i++)` ` ` `{` ` ` ` ` `// Check if the number` ` ` `// is even or not` ` ` `if` `(A[i] % 2 == 0)` ` ` `{` ` ` ` ` `// Calculate count of continuous` ` ` `// odd numbers` ` ` `K = (i - last - 1);` ` ` `// Increase the count of sub-arrays` ` ` `// with odd product` ` ` `count += (K * (K + 1) / 2);` ` ` `// Store the index of last` ` ` `// even number` ` ` `last = i;` ` ` `}` ` ` `}` ` ` `// N considered as index of` ` ` `// even number` ` ` `K = (N - last - 1);` ` ` `count += (K * (K + 1) / 2);` ` ` `return` `count;` `}` `// Driver Code` `var` `arr = [ 12, 15, 7, 3, 25,` ` ` `6, 2, 1, 1, 7 ];` `var` `n = arr.length;` `// Function call` `document.write( countSubArrayWithOddProduct(arr, n));` `// This code is contributed by rrrtnx.` `</script>` |

**Output:**

16

**Time Complexity:** *O(N)* **Auxiliary Space:** *O(1)*

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