[Tutor] IndexError: list index out of range [ Program work fine , but gives this message , guidance requested ]

[John Joseph]

Hi All 
      I am trying to find out the duplicates in a list
, as for beginning I wanted to compare the  adjacent
elements in list , for this purpose I wrote a script
for checking the adjacent elements in a list,  if same
, it prints the result that , the adjacent numbers are
same , it not  it will print  adjacent numbers are
same 
                 My program works ,  but at the end of
the program execution it throws error 

“Traceback (most recent call last):
  File "arrayduplinital.py", line 27, in ?
    if seats[j] <> seats[j+1]:
IndexError: list index out of range”

                     I tried my best to find the logic
, why this error is coming , I was not able to find
the reason ,  I request your guidance for the reason
for this error and how to avoid it 
             I am adding the code which I wrote for
this program

**************************************************************************************
"""
  find duplicates in a list
        (1) Sort the array
        (2) counter
                  i = 0
                  j = 0
        (3) for j <= length
                if seats[j] <> seats[j+1] ==> print
value j and j+1 are not same
                       else  ===>  print value j ,  j
+1 are same

"""

seats = []
i = 0
length  = int(raw_input("Enter The Lenght of the array
:  "))

while i < length:
        num = int(raw_input("Enter the Seats :  "))
        seats.append(num)
        i += 1
print seats

seats.sort()

j = 0
for j in range(length):
        if seats[j] <> seats[j+1]:
                print " The Seat", j , "And the seat",
j+1 , "value, which are", seats[j]," and", seats[j+1],
"are not same" 
        else:
                print "The Seats ",j ,"And the seats",
j+1, "Values,", seats[j], "and", seats[j+1], "are
same"
~




		
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