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Created on Sep 22, 2015   @author: wangbin ”’ #O(N*lgN) def merge(a, p, q, r):     L = a[p: q + 1]     L.append(2 ** 31)     R = a[q + 1: r + 1]     R.append(2 ** 31)     i = 0     j = 0     for k in range(p, r + 1):         # print(“%d %d %d %d %d” % (p, q, r, i, j))         if L[i] < R[j]:             a[k] = L[i]             i += 1         else:             a[k] = R[j]             j += 1   def mergeSort(a, p, r):     if p < r :         q = int((p + r) / 2)         mergeSort(a, p, q)         mergeSort(a, q + 1, r)         merge(a, p, q, r)   if __name__ == “__main__”:     a = [2, 4, 1, 6, 3, 9, 10, 5, 7, 8, 3, 1]     mergeSort(a, 0, len(a) – 1)     print(a)