蛇形矩阵

题目参考<算法竞赛入门经典>第二版第三章 3.1

#include <stdio.h>
#include <string.h>

#define N 20
int a[N][N];
int main(int argc, char **argv){
    int n;
    while(scanf("%d",&n)!=EOF){
    memset(a, 0, sizeof(a));
    int tol = 1;
    int x, y;
    x = -1;
    y = n;
    while(tol<=n*n){
        x++;
        y--;
        while( x < n && a[x][y] == 0){
        a[x++][y] = tol++;
        }// x =  n  y = n-1
        x--;
        y--;
        while(y >= 0 && a[x][y] == 0){
        a[x][y--] = tol++;
        }
        x--;
        y++;
        while(x >= 0 && a[x][y] == 0){
        a[x--][y] = tol++;
        }
        x++;
        y++;
        while( y < n && a[x][y] == 0){
        a[x][y++] = tol++;
        }
    }
    for(int i=0; i<n;i++){
        for(int j=0;j<n;j++){
        printf("%3d ",a[i][j]);
        }
        printf("
");
    }
    }
    return 0;
}