#!/usr/bin/python3
# https://theweeklychallenge.org/blog/perl-weekly-challenge-243/#TASK1
#
# Task 1: Reverse Pairs
# =====================
#
# You are given an array of integers.
#
# Write a script to return the number of reverse pairs in the given
# array.
#
# A reverse pair is a pair (i, j) where: a) 0 <= i < j < nums.length
# and b) nums[i] > 2 * nums[j].
#
## Example 1
##
## Input: @nums = (1, 3, 2, 3, 1)
## Output: 2
##
## (1, 4) => nums[1] = 3, nums[4] = 1, 3 > 2 * 1
## (3, 4) => nums[3] = 3, nums[4] = 1, 3 > 2 * 1
#
## Example 2
##
## Input: @nums = (2, 4, 3, 5, 1)
## Output: 3
##
## (1, 4) => nums[1] = 4, nums[4] = 1, 4 > 2 * 1
## (2, 4) => nums[2] = 3, nums[4] = 1, 3 > 2 * 1
## (3, 4) => nums[3] = 5, nums[4] = 1, 5 > 2 * 1
#
############################################################
##
## discussion
##
############################################################
#
# Walk the array twice (once from 0, once from the first index + 1)
# Check the condition in each case, counting the occurrences where
# the condition holds true.

def reverse_pairs(nums: list):
    print("Input: (", ", ".join(str(x) for x in nums), ")")
    result = 0
    for i in range(len(nums)):
        for j in range(i+1, len(nums)):
            if nums[i] > 2 * nums[j]:
                result += 1
    print("Output:", str(result))

reverse_pairs( [ 1, 3, 2, 3, 1 ] );
reverse_pairs( [ 2, 4, 3, 5, 1 ] );