Codeforces Round #237 (Div. 2) A~D(一)

Valera is a little boy. Yesterday he got a huge Math hometask at school, so Valera didn't have enough time to properly learn the English alphabet for his English lesson. Unfortunately, the English teacher decided to have a test on alphabet today. At the test Valera got a square piece of squared paper. The length of the side equals n squares (n is an odd number) and each unit square contains some small letter of the English alphabet.

Valera needs to know if the letters written on the square piece of paper form letter "X". Valera's teacher thinks that the letters on the piece of paper form an "X", if:

• on both diagonals of the square paper all letters are the same;
• all other squares of the paper (they are not on the diagonals) contain the same letter that is different from the letters on the diagonals.

  Help Valera, write the program that completes the described task for him.

  Input

  The first line contains integer n (3 ≤ n n is odd). Each of the next n lines contains n small English letters ― the description of Valera's paper.

  Output

  Print string "YES", if the letters on the paper form letter "X". Otherwise, print string "NO". Print the strings without quotes.

  Sample test(s) input

  5
  xooox
  oxoxo
  soxoo
  oxoxo
  xooox
  

  output

  NO
  

  input

  3
  wsw
  sws
  wsw
  

  output

  YES
  

  input

  3
  xpx
  pxp
  xpe
  

  output

  NO

  
  

  #include 
      
       
  #include 
       
         #include 
        
          #include 
         
           using namespace std; int n; char str[500][500]; bool flag=true; int main() { cin>>n; for(int i=0;i
          
           
   
           
   B. Marathon time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output 
           
   Valera takes part in the Berland Marathon. The marathon race starts at the stadium that can be represented on the plane as a square whose lower left corner is located at point with coordinates (0, 0) and the length of the side equals a meters. The sides of the square are parallel to coordinate axes.
   
           
   As the length of the marathon race is very long, Valera needs to have extra drink during the race. The coach gives Valera a bottle of drink each d meters of the path. We know that Valera starts at the point with coordinates (0, 0) and runs counter-clockwise. That is, when Valera covers a meters, he reaches the point with coordinates (a, 0). We also know that the length of the marathon race equalsnd + 0.5 meters.
   
           
   Help Valera's coach determine where he should be located to help Valera. Specifically, determine the coordinates of Valera's positions when he covers d, 2 d, ..., n d meters.
   Input 
           
   The first line contains two space-separated real numbers a and d (1 ≤ a, d ≤ 105), given with precision till 4 decimal digits after the decimal point. Number a denotes the length of the square's side that describes the stadium. Number d shows that after each d meters Valera gets an extra drink.
   
           
   The second line contains integer n (1 ≤ n ≤ 105) showing that Valera needs an extra drink n times.
   Output 
           
   Print n lines, each line should contain two real numbers xi and yi, separated by a space. Numbers xi and yi in the i-th line mean that Valera is at point with coordinates (xi, yi) after he covers i d meters. Your solution will be considered correct if the absolute or relative error doesn't exceed 10 - 4.
   
           
   Note, that this problem have huge amount of output data. Please, do not use cout stream for output in this problem.
   Sample test(s) input 
           
  2 5
  2
   output 
           
  1.0000000000 2.0000000000
  2.0000000000 0.0000000000
   input 
           
  4.147 2.8819
  6
   output 
           
  2.8819000000 0.0000000000
  4.14700000