pythongridcrossword

How to find a word in a 2d grid?


This is the problem i was given to solve: Write a function searchDirection(word, row, col, direction, grid) that takes a word to find, a row and column starting position, a direction string such as "down", and a grid, and searches for the word in the given direction only, from the given starting position. If the word is found, a message is printed and True is returned. Otherwise, nothing is printed and False is returned.

I'm supposed to use nested for loops... but I don't know how to structure them?

Here are what the outputs should look like:

searchDirection("frog", 0, 5, "down", g) should print “frog found at (0, 5) going down” and return True

searchDirection("frog", 0, 5, "right", g) should return False, without printing anything


Solution

  • Here is a solution using a while loop, I will leave it as an exercise for you to figure out how to convert the logic into "nested for loops" (Hint: Take a look at the More Control Flow Tools section of the official documentation):

    def searchDirection(word, row, col, direction, grid):
        m = len(grid)
        if not m:
            return False
    
        n = len(grid[0])
        if not n:
            return False
    
        directions = {
            "up": (-1, 0),
            "right": (0, 1),
            "down": (1, 0),
            "left": (0, -1)
        }
        if direction not in directions:
            return False
    
        i = 0
        r, c = row, col
        while i < len(word) and 0 <= r < m and 0 <= c < n:
            if grid[r][c] != word[i]:
                return False
            r += directions[direction][0]
            c += directions[direction][1]
            i += 1
    
        if i == len(word):
            print(f"{word} found at ({row}, {col}) going {direction}")
    
        return i == len(word)
    
    
    g = [['a', 'b', 'c', 'd', 'e', 'f'],
         ['a', 'b', 'c', 'd', 'e', 'r'],
         ['a', 'b', 'c', 'd', 'e', 'o'],
         ['a', 'b', 'c', 'd', 'e', 'g'],
         ['a', 'b', 'c', 'd', 'e', 'f'],
         ['a', 'b', 'c', 'd', 'e', 'f']]
    
    print(searchDirection("frog", 0, 5, "down", g))
    print(searchDirection("frog", 0, 5, "right", g))
    

    Output:

    frog found at (0, 5) going down
    True
    False