# Print number of even sum sub-arrays of an array

**Problem:** For a given array of positive or negative integers, find count of sub-arrays whose sum is even.

**Problem Explanation:** For a given array **a** ={1, -2, 3, 4, -5}, even sum sub-arrays are {-2}, {3, 4, -5}, {-2 , 3, 4, -5}, {4}, {1, -2, 3}, {1, -2, 3, 4}. Hence, **output** will be 6.

**Java Implementation**

public int evenSumSubArrays(int arr[]) { int[] count = new int[2]; int sum = 0; for (int i = 0; i < arr.length; i++) { sum = (sum + arr[i]) % 2; count[Math.abs(sum)]++; } //Total even sum arrays = Total even sub arrays + number of odd pairs //+ number of even only pairs int totalEvenSumSubArrayCount = count[0] + (count[0] * (count[0] - 1) / 2) + (count[1] * (count[1] - 1) / 2); return (totalEvenSumSubArrayCount); }

**TimeComplexity: O(n)**

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