i was solving this problem "https://mirror.codeforces.com/problemset/problem/629/A" but i did not understand the 2nd testcase i think the output should be 8 not 9
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i was solving this problem "https://mirror.codeforces.com/problemset/problem/629/A" but i did not understand the 2nd testcase i think the output should be 8 not 9
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answer is 3 on the second column
You are calculating pairs of chocolates that share the same row and column. In second example:
1st row has 1 pair:
{(1,1) , (1,2)}
2nd row has 3 pairs:
{(2, 1), (2, 3)}, {(2, 1), (2, 4)} , {(2,3), (2,4)}
3rd row has 1 pair:
{(3, 3), (3, 4)}
4th row has no pairs because it has only 1 element;
All columns have only 1 pair each:
1st:
{(1, 1), (2, 1)}
2nd:{(1, 2), (4, 2)}
3rd:{(2, 3), (3, 3)}
4th:{(2, 4), (3, 4)}
Counting all pairs we get:
sol = 1 + 3 + 1 + 0 + 1 + 1 + 1 + 1 = 9
In case you don't know, there is also a formula for calculating pairs in single column/row
n = number of chocolates in given row/column
sol = n * (n - 1) / 2