Sum of the series 1 , 2 , 4 , 3 , 5 , 7 , 9 , 6 , 8 , 10 , 11 , 13. . till N | Java program to implement the above approach ; Function to find the sum of first N odd numbers ; Function to find the sum of first N even numbers ; Function to overall find the sum of series ; Initial odd numbers ; Initial even numbers ; First power of 2 ; Check for parity for odd / even ; Counts the sum ; Get the minimum out of remaining num or power of 2 ; Decrease that much numbers from num ; If the segment has odd numbers ; Summate the odd numbers By exclusion ; Increase number of odd numbers ; If the segment has even numbers ; Summate the even numbers By exclusion ; Increase number of even numbers ; Next set of numbers ; Change parity for odd / even ; Driver code
class GFG { static int sumodd ( int n ) { return ( n * n ) ; } static int sumeven ( int n ) { return ( n * ( n + 1 ) ) ; } static int findSum ( int num ) { int sumo = 0 ; int sume = 0 ; int x = 1 ; int cur = 0 ; int ans = 0 ; while ( num > 0 ) { int inc = Math . min ( x , num ) ; num -= inc ; if ( cur == 0 ) { ans = ans + sumodd ( sumo + inc ) - sumodd ( sumo ) ; sumo += inc ; } else { ans = ans + sumeven ( sume + inc ) - sumeven ( sume ) ; sume += inc ; } x *= 2 ; cur ^= 1 ; } return ans ; } public static void main ( String [ ] args ) { int n = 4 ; System . out . println ( findSum ( n ) ) ; } }