Python program to Occurrences of i before first j in list

Given a list, the task is to write a Python program to count the occurrences of i^th element before the first occurrence of j^th element.

Examples:

Input : test_list = [4, 5, 6, 4, 1, 4, 8, 5, 4, 3, 4, 9], i, j = 4, 8 
Output : 3 
Explanation : 4 occurrs 3 times before 8 occurs.

Input : test_list = [4, 5, 6, 4, 1, 4, 8, 5, 4, 3, 4, 9], i, j = 5, 8 
Output : 1 
Explanation : 5 occurrs 1 time before 8 occurs. 

Method #1 : Using loop.

In this, we increment counter whenever i is encountered and stop when any j has occurred, i.e breaking from the loop.

Python3

# Python3 code to demonstrate working of
# Occurrences of i before first j
# Using loop

# initializing Matrix
test_list = [4, 5, 6, 4, 1, 4, 8, 5, 4, 3, 4, 9]

# printing original list
print("The original list is : " + str(test_list))

# initializing i, j
i, j = 4, 8

res = 0
for ele in test_list:

    # breaking on 1st j
    if ele == j:
        break

    # counting i till 1st j
    if ele == i:
        res += 1

# printing result
print("Number of i's till 1st j : " + str(res))

Output:

The original list is : [4, 5, 6, 4, 1, 4, 8, 5, 4, 3, 4, 9]
Number of i's till 1st j : 3

Method #2 : Using index() + slicing + count()

In this, we perform the task of getting the index of j, and then slice list till there, count() is used to get a count of i in the sliced list to get the required result.

Python3

# Python3 code to demonstrate working of
# Occurrences of i before first j
# Using index() + slicing + count()

# initializing Matrix
test_list = [4, 5, 6, 4, 1, 4, 8, 5, 4, 3, 4, 9]

# printing original list
print("The original list is : " + str(test_list))

# initializing i, j
i, j = 4, 8

# getting index
jidx = test_list.index(j)

# slicing list
temp = test_list[:jidx]

# getting count
res = temp.count(i)

# printing result
print("Number of i's till 1st j : " + str(res))

Output:

The original list is : [4, 5, 6, 4, 1, 4, 8, 5, 4, 3, 4, 9]
Number of i's till 1st j : 3