### Medeali's blog

By Medeali, history, 6 months ago,

i was solving this problem "https://codeforces.com/problemset/problem/629/A" but i did not understand the 2nd testcase i think the output should be 8 not 9

• 0

 » 6 months ago, # | ← Rev. 2 →   0
•  » » 6 months ago, # ^ |   0 answer is 3 on the second column
•  » » » 6 months ago, # ^ |   0 Yep, my bad.
 » 6 months ago, # | ← Rev. 2 →   0 pieces that share the same row are: $\newline$ (1,1) and (1,2) $\newline$ (2,1) and (2,4) $\newline$ (3,2) and (3,3) $\newline$ (4,2) and (4,3) $\newline$ pieces that share the same column are: $\newline$ (1,1) and (2,1) $\newline$ (1,2) and (3,2) $\newline$ (1,2) and (4,2) $\newline$ (3,2) and (4,2) $\newline$ (3,3) and (4,3) $\newline$ The total is 9. $\newline$ I think you made a little mistake by not counting the 3 possible combinations in column 2.
•  » » 6 months ago, # ^ |   0 thanks you are right i only counted adjacent ones
 » 6 months ago, # |   0 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 = 9In case you don't know, there is also a formula for calculating pairs in single column/row Formulan = number of chocolates in given row/column sol = n * (n - 1) / 2