Problem description
Fox Ciel starts to learn programming. The first task is drawing a fox! However, that turns out to be too hard for a beginner, so she decides to draw a snake instead.
A snake is a pattern on a n by m table. Denote c-th cell of r-th row as (r, c). The tail of the snake is located at (1, 1), then it's body extends to (1, m), then goes down 2 rows to (3, m), then goes left to (3, 1) and so on.
Your task is to draw this snake for Fox Ciel: the empty cells should be represented as dot characters ('.') and the snake cells should be filled with number signs ('#').
Consider sample tests in order to understand the snake pattern.
Input
The only line contains two integers: n and m (3 ≤ n, m ≤ 50).
n is an odd number.
Output
Output n lines. Each line should contain a string consisting of m characters. Do not output spaces.
Examples
Input
3 3
Output
###
..#
###
Input
3 4
Output
####
...#
####
Input
5 3
Output
###
..#
###
#..
###
Input
9 9
Output
#########
........#
#########
#........
#########
........#
#########
#........
#########
解题思路：按规律输出，当i为奇数时，输出的一行全部为'#'；当i为偶数时，用flag做开关，交换输出两种格式，水过！
AC代码：
1 #include<bits/stdc++.h> 2 using namespace std; 3 #define FOR(a,b,c) for(int i=a;i<=b;++i)printf("%c",c) 4 int n,m;bool flag; 5 int main(){ 6 cin>>n>>m;flag=false; 7 for(int i=1;i<=n;++i){ 8 if(i%2)FOR(1,m,'#'); 9 else{ 10 if(!flag){FOR(1,m-1,'.');cout<<'#';flag=true;} 11 else{cout<<'#';FOR(2,m,'.');flag=false;} 12 } 13 cout<<endl; 14 } 15 return 0; 16 }