SUMFOUR  4 values whose sum is 0
The SUM problem can be formulated as follows: given four lists A, B, C, D of integer values, compute how many quadruplet (a, b, c, d ) belongs to A x B x C x D are such that a + b + c + d = 0 . In the following, we assume that all lists have the same size n
Input
The first line of the input file contains the size of the lists n (this value can be as large as 4000). We then have n lines containing four integer values (with absolute value as large as 2^{28} ) that belong respectively to A, B, C and D .
(Edited: n <= 2500)
Output
Output should be printed on a single line.
Example
Input: 6 45 22 42 16 41 27 56 30 36 53 37 77 36 30 75 46 26 38 10 62 32 54 6 45 Output: 5
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nadstratosfer:
20190724 04:56:34
Sadly, some datasets have nearly no zerosumming quadruplets, rendering a large assortment of possible optimizations useless. Most people commenting here seem to confuse optimization with not doing stupid stuff, and noone claiming to have done it in O(n^2) has runtime to prove it. I'm still bothered to find the efficient approach candide hinted to, but other than that the problem seems like a waste of time after getting the green bar. 

yashranjan74:
20190621 11:18:25
Just use equal range in place of unordered_map. Although the complexity was better using unordered_map but equal_range get AC whereas unordered_map gave TLE. 

harry_shit:
20190604 12:10:34
tle for O(n*n) also,using unordered map


hetp111:
20190601 09:02:24
How did 1st ranker got it in 0.01sec? mine took 2+sec with O(n*n*log(n))... Last edit: 20190601 09:04:09 

abhinav_jain02:
20190518 08:28:58
Note that equal elements in a list are considered to be distinct 

mikroz:
20190413 13:19:50
gp_hash_table 

sagar_june97p:
20190412 20:07:25
unordered_map got me TLE, however equal_range passed.


prudhvi_495:
20190407 13:20:45
Last edit: 20190414 08:06:25 

syed_tanveer:
20190403 12:40:58
AC in first go using upper_bound() and lower_bound() 

Rahul Kathuria:
20190403 03:44:13
Easy peasy :P AC in 1st go!

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