# 50050. Spiral Snake

## I'm a slow walker, but I never walk backwards.

Write a function SpiralSnake to fill a matrix in a snake-like order.

Suppose we have an $N$ by $N$ grid, $G$ like the following.

p10139. $G\lbrack N]\lbrack N]$

If we go from the center of the matrix and enumerate the elements in clockwise spiral order, we will have a vector of elements like the following.

p10139. $snake\lbrack N^2]$

Now given the snake array, we would like to construct the original matrix $G$, then put the elements back into a result array in a row by row, column by column manner, like the following.

p10139. $result\lbrack N^2]$

The prototype of the function you need to implement is as follows.

1void SpiralSnake(int N, int *snake, int *result);


The main.c program is as follow:

1234567891011121314151617181920#include <stdio.h>#include "SpiralSnake.h"#include <assert.h> #define MAXLEN 1000 static int snake[MAXLEN*MAXLEN];static int result[MAXLEN*MAXLEN]; int main(){    int N;    while(scanf("%d", &N)!=EOF){        for(int i=0; i<N*N; i++)              assert(scanf("%d", &snake[i])==1);        SpiralSnake(N, snake, result);        for(int i=0; i<N*N; i++)             printf("%d%c", result[i], " \n"[i==N*N-1]);    }    return 0;}


The header file SpiralSnake.h is as follows:

1234#ifndef SPIRALSNAKE_H_INCLUDED#define SPIRALSNAKE_H_INCLUDEDvoid SpiralSnake(int N, int *snake, int *result);#endif


## Input Format

Input contains multiple test cases, each test case has 2 lines.

The first line in a test case contains one integer, $N$, meaning the matrix size is $N$ by $N$. Then next line contains $N^2$ integers indicating the elements of the snake.

### Technical limitation

• $N$ is odd and $1 \le N \le 999$

## Output Format

Print out the result.

## Sample Input

31 2 3 4 5 6 7 8 936 8 10 9 16 15 18 23 29


## Sample Output

3 4 5 2 1 6 9 8 710 9 16 8 6 15 29 23 18


## Note

You can use Ctrl+Z (in Windows) or Ctrl+D (in Linux) to input the end-of-file (EOF) character.

## Compile

gcc -std=c99 -O2 -c main.c -lmgcc -std=c99 -O2 -c SpiralSnake.c -lmgcc -std=c99 -O2 SpiralSnake.o main.o -lm