import numpy as np
import math
B = 8192
r = 9


def distinguish(ctxt_blocks):
    R_i = np.zeros((256, 16))
    for c_blk in ctxt_blocks:
        for i in xrange(16):
            R_i[ord(c_blk[i]), i] +=1
    chi_sq = 0
    rows, cols = R_i.shape
    for i in xrange(rows):
        for j in xrange(cols):
            E_i = B/float(256)
            chi_sq +=  (E_i - R_i[i, j])**2 / E_i
    mean_cs = (rows*cols) - 1
    std_cs = math.sqrt(2*mean_cs)
    if abs(chi_sq - mean_cs) > 3*std_cs :
        return 0
    else :
        return 1