Number of subarrays having sum exactly equal to k | Java program to find number of subarrays with sum exactly equal to k . ; Function to find number of subarrays with sum exactly equal to k . ; HashMap to store number of subarrays starting from index zero having particular value of sum . ; Sum of elements so far . ; Add current element to sum so far . ; If currsum is equal to desired sum , then a new subarray is found . So increase count of subarrays . ; currsum exceeds given sum by currsum - sum . Find number of subarrays having this sum and exclude those subarrays from currsum by increasing count by same amount . ; Add currsum value to count of different values of sum . ; Driver Code
import java . util . HashMap ; import java . util . Map ; public class GfG { static int findSubarraySum ( int arr [ ] , int n , int sum ) { HashMap < Integer , Integer > prevSum = new HashMap < > ( ) ; int res = 0 ; int currsum = 0 ; for ( int i = 0 ; i < n ; i ++ ) { currsum += arr [ i ] ; if ( currsum == sum ) res ++ ; if ( prevSum . containsKey ( currsum - sum ) ) res += prevSum . get ( currsum - sum ) ; Integer count = prevSum . get ( currsum ) ; if ( count == null ) prevSum . put ( currsum , 1 ) ; else prevSum . put ( currsum , count + 1 ) ; } return res ; } public static void main ( String [ ] args ) { int arr [ ] = { 10 , 2 , - 2 , - 20 , 10 } ; int sum = - 10 ; int n = arr . length ; System . out . println ( findSubarraySum ( arr , n , sum ) ) ; } }