Detection of change in consecutive list elements isn't working

July 13, 2022

My goal is to print the value of the elements in the list where the consecutive elements are changed. For instance, if the given input is 1 1 1 3 3 3 2 then the output should be [1,3,3,2], because in the input you can see that the value of 1 is changing to 3, so 1 and 3 should be appended to the list, and also the value of 3 is changing to 2, so 3 and 2 should also be appended to the list.

The required output is [1,3,3,2].
However, my code is returning only [1,3] but not [3,2]. I don’t understand why?

for t in range(int(input())):
    n = int(input())
    a = list(map(int,input().split()))[:n]
    l=[]
    if a.count(a[0])==len(a):
        print("0")
    else:
        for i in a:
            if a[i] != a[i+1]:
                print(i)
                l.extend((a[i],a[i+1]))
        print(l)

>Solution :

Code:

a = [1, 1, 1, 3, 3, 3, 2]
output = []
for i in range(len(a) - 1):
    if a[i] != a[i + 1]:
        output.append(a[i])
        output.append(a[i+1])

print(output)

Output: