Why do I get list index out of range even though I've kept a condition to check so?

Question

I'm getting list index out of range even though I've kept a condition so that it would not check such a state where the index is not inside the limit specified. Please go through the code below.

T=int(input())
c=1;
f=0;
d=[]
for i in range(T):
    a=int(input())
    A=list(map(int, input().strip().split()))
    b=int(input())
    B=list(map(int, input().strip().split()))
    for j in range(a-1):
        for k in range(b):
            if(A[j] == B[k]):
                if(j+c < a, k+c< b):
                    while(f==0):
                            if(j+c < a, k+c < b):
                                c += 1
                                if(A[j+c]==B[k+c]):
                                    f=1
                if(f==0):            
                    d.append(c)
        f=0;
        c=1;
    d.sort;
    d= []
    print (d[-1])

This is the error that I get:

    Runtime Error:
Runtime ErrorTraceback (most recent call last):
  File "/home/a065c7cd2e000ec65fe6b148ca7dee08.py", line 17, in <module>
    if(A[j+c]==B[k+c]):
IndexError: list index out of range

I was trying to solve the question of Longest Common Increasing Subsequence. It would be helpful if the correct for it would be provided otherwise. :)

Given two arrays, find length of the longest common increasing subsequence (LCIS). For example length of LCIS for A[] = {3, 4, 9, 1} and B[] = {5, 3, 8, 9, 10, 2, 1} is 2 ( The subsequence {3, 9} is the longest subsequence that is both common and increasing. As another example LCIS for A[] = {1, 1, 4, 3} and B[] = {1, 1, 3, 4} is 2 (There are two subsequences {1, 4} and {1, 3}).

Answer 1

First, the statement if(a, b): is not the same as if(a and b): , as if(a, b): is checking whether the tuple (a, b) is empty or not, and since it is not empty, it returns true no matter what. Try

if(False, False):
    print('What?!')

and see that the print does execute.

For your question, within your code you have this:

if(j+c < a and k+c < b):
    c += 1
    if(A[j+c]==B[k+c]):

so, suppose that j+c is 1 and a is 2, we'd enter the block. Then, we add one to c , so now j+c is 2, and a is 2, and then we'd check A[2] which is out of bounds.

And as a side note, you can use the len function to get the length of a list. So your input could look like:

A=list(map(int, input('A:').strip().split()))
B=list(map(int, input('B:').strip().split()))
a, b = len(A), len(B)