CodeForces is a nice website for anyone, who likes checking himself vs the top developers worldwide. It’s even separated into divisions, thus, they kindly provide 3 easy questions and 5 hard. Although, I do not know anyone who can call the first 3 questions of the 2. division *easy*. Although usually the answer comes within less than 15 minutes. In some of them.

Thus, I will simply show the first question in the first division. It was something like this:

*Okabe needs to renovate the Future Gadget Laboratory after he tried doing some crazy experiments! The lab is represented as an n by nsquare grid of integers. A good lab is defined as a lab in which every number not equal to 1 can be expressed as the sum of a number in the same row and a number in the same column. In other words, for every x, y such that 1 ≤ x, y ≤ n and a _{x, y} ≠ 1, there should exist two indices s and t so that a_{x, y} = a_{x, s} + a_{t, y}, where a_{i, j} denotes the integer in i-th row and j-th column.*

*Help Okabe determine whether a given lab is good!*

*Input*

*The first line of input contains the integer n (1 ≤ n ≤ 50) — the size of the lab.*

*The next n lines contain n space-separated integers denoting a row of the grid. The j-th integer in the i-th row is a _{i, j} (1 ≤ a_{i, j} ≤ 10^{5}).*

*Output*

*Print “Yes” if the given lab is good and “No” otherwise.*

*You can output each letter in upper or lower case.*

Long story short, you have a matrix and you should say whether it is possible for each value in the matrix to be represented as a sum of one value in the same column and one value in the same row. At least this is what I understood from the first reading.

Whenever we have iteration of a matrix, these are two nested loops. Which is a complexity of N^2. However, we also have to check a given line and a given column within the matrix, for the sum. This makes the complexity up to N^4. And two more nested loops inside ours. I really was pretty curious whether such an ugly solution should work, thus I have decided to try it out:

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using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; class Startup { static void Main() { int n = int.Parse(Console.ReadLine()); List<List<int>> myList = new List<List<int>>(); string strResult = "Yes"; for (int i = 0; i < n; i++) { myList.Add(ReadLineAndParseToList()); } int intValueToCompare = 0; for (int i = 0; i < n; i++) { for (int k = 0; k < n; k++) { if (myList[i][k]!=1) { intValueToCompare = myList[i][k]; bool bZeroAchieved = false; for (int ii = 0; ii < n; ii++) { for (int kk = 0; kk < n; kk++) { if (ii!=i && kk!=k) { if(intValueToCompare - myList[i][kk] - myList[ii][k]==0) { bZeroAchieved = true; } } } } if (!bZeroAchieved) strResult = "No"; } } } Console.WriteLine(strResult); } public static List<int> ReadLineAndParseToList() { return Console.ReadLine().Split().Select(int.Parse).ToList(); } } |

Well, it worked! 🙂 Cheers! 🙂