How to find a duplicate element in an array

Author: bigbighd604

problems/dup_element_in_array/find_dup_elem.py

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+#!/usr/bin/env python
+
+#Suppose you have an array of 1001 integers. The integers are in random order,
+# but you know each of the integers is between 1 and 1000 (inclusive).
+# In addition, each number appears only once in the array, except for
+# one number, which occurs twice. Assume that you can access each element
+# of the array only once. Describe an algorithm to find the repeated number.
+# If you used auxiliary storage in your algorithm, can you find an algorithm
+# that does not require it?
+
+import random
+import sys
+
+def GenArray(length):
+  array = range(1,length + 1)
+  dup = random.randint(1, length)
+  print 'Dup num generated: %s' % dup
+  array.append(dup)
+  random.shuffle(array)
+  return array
+
+def XorFind(array):
+  print 'Start Xor find ...'
+  found = 0
+  for i, item in enumerate(array):
+    found = found ^ item ^ i
+  # An alternative:
+  #for i in xrange(1, length + 2):
+  #  found = found ^ array[i-1] ^ (i - 1)
+  print 'Dup num founded (Xor): %s' % found
+
+def SumFind(array):
+  print 'Start Sum find ...'
+  length = len(array)
+  expect_sum = (1 + length - 1) * (length - 1) / 2
+  real_sum = reduce(lambda x, y : x + y, array)
+  print 'Dup num founded (Sum): %s' % (real_sum - expect_sum)
+
+if __name__ == '__main__':
+  length = int(sys.argv[1])
+  array = GenArray(length)
+  XorFind(array)
+  SumFind(array)