#include <stdio.h>
#include <string.h>
#include <mpi.h>
#include <stdlib.h>
#include <assert.h>

int main(int argc, char* argv[])
{
        int rank;
        int nprocs;
        MPI_Status status;

        MPI_Init(&argc, &argv);
        MPI_Comm_rank(MPI_COMM_WORLD, &rank);
        MPI_Comm_size(MPI_COMM_WORLD,&nprocs);

        int size = nprocs;
        int *send_size = new int [size];
        assert(send_size!=NULL);
        int *recv_size = new int [size];
        assert(recv_size!=NULL);
        int *send_pos = new int [size];
        assert(send_pos!=NULL);
        int *recv_pos = new int [size];
        assert(recv_pos!=NULL);
	int send_sum=0, recv_sum=0;

	for(int i=0;i<size;i++)
	{
		send_size[i] = recv_size[i] = 2000000;
	}			

	for(int i=0;i<size;i++)	
	{
		send_sum += send_size[i];
		recv_sum += recv_size[i];
	}

	send_pos[0] = recv_pos[0] = 0;
	for(int i=1;i<size;i++)
	{
		send_pos[i] = send_pos[i-1] + send_size[i];
		recv_pos[i] = recv_pos[i-1] + recv_size[i];
	}

	// Total Mem = 1M * 20 * 2 * 8 * 16 = 5G 	
	unsigned long long *send_buf = new unsigned long long [send_sum];
	unsigned long long *recv_buf = new unsigned long long [recv_sum];

	for(int i=0;i<send_sum;i++)	send_buf[i] = i;

	MPI_Alltoallv(send_buf, send_size, send_pos, MPI_LONG_LONG_INT, recv_buf, recv_size, recv_pos, MPI_LONG_LONG_INT, MPI_COMM_WORLD); 	
		

        MPI_Finalize();
        return 0;
}