C#小技巧

1）求全排列，采用递归分析，刚开始忘了 将数组恢复原样，结果运行半天都是错误：

 private void button2_Click(object sender, EventArgs e)
        {
            perm(a, 0, 2);
        }
        private void perm(int[] list, int i, int n)
        {
            int j;

            if (i == n)
            {
                listprint(list);
            }
            else
            {
                for (j = i; j <= n; j++)
                {
                    SWAP(ref list[i], ref list[j]);
                    perm(list, i + 1, n);
                    SWAP(ref list[i], ref list[j]);//一定要将数组恢复原样
                }
            }
        }
        private void SWAP(ref int a, ref int b)
        {
            int c = a;
            a = b;
            b = c;
        }

2）arraylist添加结构体单元时时，不需要每次都new一个结构体单元

 public struct pcoordinate
        {
            public int pX;
            public int pY;
        }
        ArrayList lt = new ArrayList();
        private void button1_Click(object sender, EventArgs e)
        {
            pcoordinate pc = new pcoordinate();
            pc.pX = 1;
            pc.pY = 1;
            lt.Add(pc);
            //不需要重新new一个pcoordinate，直接修改值添加到arraylist，不会改变原来的值
            pc.pX = 2;
            pc.pY = 2;
            lt.Add(pc);

            pc.pX = 3;
            pc.pY = 3;
            lt.Add(pc);

            foreach (pcoordinate p in lt)
            {
                listBox1.Items.Add(p.pX.ToString() + " " + p.pY.ToString());
            }
        }

结果：1   1

        2   2

        3   3

而不是1   1

        1   1

        1   1