def gridChallenge(grid):
    grid = [sorted(s) for s in grid]   
     
    for c in range(len(grid[0])):
        c_str = [row[c] for row in grid]
        
        for i in range(1, len(c_str)):
            if c_str[i-1] > c_str[i]:
                return "NO"
            
    return "YES"