Count pairs in array whose sum is divisible by 4 | Java program to count pairs whose sum divisible by '4' ; Program to count pairs whose sum divisible by '4' ; Create a frequency array to count occurrences of all remainders when divided by 4 ; Count occurrences of all remainders ; If both pairs are divisible by '4' ; If both pairs are 2 modulo 4 ; If one of them is equal to 1 modulo 4 and the other is equal to 3 modulo 4 ; Driver code
import java . util . * ; class Count { public static int count4Divisibiles ( int arr [ ] , int n ) { int freq [ ] = { 0 , 0 , 0 , 0 } ; int i = 0 ; int ans ; for ( i = 0 ; i < n ; i ++ ) ++ freq [ arr [ i ] % 4 ] ; ans = freq [ 0 ] * ( freq [ 0 ] - 1 ) / 2 ; ans += freq [ 2 ] * ( freq [ 2 ] - 1 ) / 2 ; ans += freq [ 1 ] * freq [ 3 ] ; return ( ans ) ; } public static void main ( String [ ] args ) { int arr [ ] = { 2 , 2 , 1 , 7 , 5 } ; int n = 5 ; System . out . print ( count4Divisibiles ( arr , n ) ) ; } }