蛇形矩阵     面试算法（1）

前段时间微信订阅号收到一个关于算法的面试题，是让实现一个N阶的蛇形矩阵。
题中所给图为如下的正方形。



分析：观察可知图中数据排列规律。 1. 数据从最右边一列开始，由上至下至最后一行； 2. 由最下一行自右向左，至最左端；
3. 与 1 顺序相反，由下至上至第一行；
4. 与 2 顺序相反，由左至右至倒数第二列；
5. 依次执行1,2,3,4 至 矩阵填满，或当前数据至达到N*N。
注：图中数据只可被赋值依次，且沿顺时针方向变化。

/**
* project  Algorithm
* package  finish
* fileInfo SnakeMartix.java  2014-3-29 下午1:21:48
* author   WANGXIN
* aim      TODO
*/
package finish;
import java.util.Scanner;
/**
* @author WANGXIN by 2014-3-29下午1:21:48
* @version v1.0
*/
public class SnakeMartix {
public static void main(String[] args) {
int M;
int N;
System.out
.println("Please input the Snake-Matrix`s rows and columns: ");
System.out.print("rows = ");
@SuppressWarnings("resource")
Scanner scanner = new Scanner(System.in);
M = scanner.nextInt();
System.out.print("columns = ");
N = scanner.nextInt();
System.out.println("Snake-Matrix(" + M + " , " + N + ")");
printSnake(M, N);
}
/**
* display the Snake-Matrix
*
* @param M
*            the row of the Matrix
* @param N
*            the columns of the Matrix
*/
public static void printSnake(int M, int N) {
int num = 0;
int i = 0;
int j = 0;
int x = 0;
int y = 0;
int[][] arr = new int[M]
;
char[][] str = new char[M]
;
int min = M > N ? N : M;
min = (int)Math.round(min / 2.0 + 0.5);
while (true) {
for (i = x; i <= M - 1 - x; i++) {
if (num == M * N)
break ;
arr[i][N - 1 - y] = ++num;
str[i][N - 1 - y] = '↓';
}
y++;// decrease y line(s)
for (j = N - 1 - y; j >= y - 1; j--) {
if (num == M * N)
break ;
arr[M - y][j] = ++num;
str[M - y][j] = '←';
}
x++;// decrease x line(s)
for (i = M - 1 - x; i >= x - 1; i--) {
if (num == M * N)
break ;
arr[i][y - 1] = ++num;
str[i][y - 1] = '↑';
}
for (j = y; j < N - y; j++) {
if (num == M * N)
break ;
arr[y - 1][j] = ++num;
str[y - 1][j] = '→';
}
if (y == min || x == min) {
//              System.out.println("x = " + x  + " y = "+ y);//label is not the most efficient
break;
}
}
System.out.println();
for (int k = 0; k < M; k++) {
for (int k2 = 0; k2 < N; k2++) {
System.out.print(arr[k][k2] + "\t");
}
System.out.println();
}
System.out.println();
System.out.println("-----------direction show as follow------------");
for (int k = 0; k < M; k++) {
for (int k2 = 0; k2 < N; k2++) {
System.out.print(str[k][k2] + "\t");
}
System.out.println();
}
}
}