Find the cordinates of the fourth vertex of a rectangle with given 3 vertices in Python

Suppose we have a grid of size Q * P, this grid contains exactly three asterisk '*' and every other cell there is dot '.', where '*' is for a vertex of a rectangle. We have to find the coordinates of the missing vertex. Here we will consider 1-based indexing.

So, if the input is like grid = [ ".*.", "...", "*.*" ], then the output will be [1, 3], this is the missing coordinate.

To solve this, we will follow these steps −

• p := number of rows

• q := number of columns

• row := make a map for all row number, and associated value is 0

• col := make a map for all column number, and associated value is 0

• for i in range 0 to p, do

  • for j in range 0 to q, do

    • if grid[i, j] is same as '*', then

      • row[i] := row[i] + 1

      • col[j] := col[j] + 1

  • for each k,v in row, do

    • if v is same as 1, then

      • x_coord := k;

  • for each k,v in col, do

    • if v is same as 1, then

      • y_coord := k;

• return(x_coord + 1, y_coord + 1)

Example 

Let us see the following implementation to get better understanding −

def get_missing_vertex(grid) :
   p = len(grid)
   q = len(grid[0])
   row = dict.fromkeys(range(p), 0)
   col = dict.fromkeys(range(q), 0)
   for i in range(p) :
      for j in range(q) :
         if (grid[i][j] == '*') :
            row[i] += 1
            col[j] += 1
   for k,v in row.items() :
      if (v == 1) :
         x_coord = k;
   for k,v in col.items() :
      if (v == 1) :
         y_coord = k;
   return (x_coord + 1, y_coord + 1)
grid = [".*.", "...", "*.*"]
print(get_missing_vertex(grid))

Input

[".*.", "...", "*.*"]

Output

(1, 3)