回形遍历（螺旋遍历）实现-C语言版

最近帮同学写一个二维数组的回形遍历，看了一下，没什么好思路，百度，google了一把，使用递归算法还是比较好理解的，记录已备用
1 什么是螺旋遍历？
2 实现的思路是递归： 
Solution: There are several ways to solve this problem, but I am mentioning a method that is intuitive to understand and easy to implement. The idea is to consider the matrix similar to onion which can be peeled layer after layer. We can use the same approach to print the outer layer of the matrix and keep doing it recursively on a smaller matrix (with 1 less row and 1 less column).
图形理解：
3 C语言实现： 

#include <stdio.h>
#include <stdlib.h>
void print_layer_top_right(int a[][4], int col, int row, int collen, int rowlen);
void print_layer_bottom_left(int a[][4], int col, int row, int collen, int rowlen);

int main(void)
{
int a[5][4] = {
{1,2,3,4},
{5,6,7,8},
{9,10,11,12},
{13,14,15,16},
{17,18,19,20}
};

print_layer_top_right(a,0,0,3,4);
exit(0);
}

//
// prints the top and right shells of the matrix
//
void print_layer_top_right(int a[][4], int col, int row, int collen, int rowlen)
{
int i = 0, j = 0;

// print the row
for(i = col; i<=collen; i++)
{
printf("%d,", a[row][i]);
}

//print the column
for(j = row + 1; j <= rowlen; j++)
{
printf("%d,", a[j][collen]);
}

// see if we have more cells left
if(collen-col > 0)
{
// 'recursively' call the function to print the bottom-left layer
print_layer_bottom_left(a, col, row + 1, collen-1, rowlen);
}
}

//
// prints the bottom and left shells of the matrix

void print_layer_bottom_left(int a[][4], int col, int row, int collen, int rowlen)
{
int i = 0, j = 0;

//print the row of the matrix in reverse
for(i = collen; i>=col; i--)
{
printf("%d,", a[rowlen][i]);
}

// print the last column of the matrix in reverse
for(j = rowlen - 1; j >= row; j--)
{
printf("%d,", a[j][col]);
}

if(collen-col > 0)
{
// 'recursively' call the function to print the top-right layer
print_layer_top_right(a, col+1, row, collen, rowlen-1);
}
}

4 ref: 
http://shashank7s.blogspot.com/2011/04/wap-to-print-2d-array-matrix-in-spiral.html