算法

public class MainActivity extends AppCompatActivity {

    EditText mynum;
    Button start,start2,start3;
    TextView end;
    String str="";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mynum = (EditText) findViewById(R.id.num);
        start = (Button) findViewById(R.id.start1);
        start2 = (Button) findViewById(R.id.start2);
        start3 = (Button) findViewById(R.id.start3);
        end = (TextView) findViewById(R.id.end);

//杨辉三角
        start.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String s = mynum.getText().toString();
                int num = Integer.parseInt(s);
                if (num > 0) {
                    int[][] a = new int[num][num];
                    // 将每行的第一个数和最后一个数都赋为1
                    for (int i = 0; i < num; i++) {
                        a[i][0] = 1;
                        a[i][i] = 1;
                    }
                    // 当行数大于2的时候就可以使用递推公式
                    if (num > 2) {
                        // 依次将中间某个数的值赋为其上面紧邻着的两个数的和
                        for (int i = 2; i < num; i++) {
                            for (int j = 1; j < num - 1; j++) {
                                a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
                            }
                        }
                    }
                    // 依次输出这些数
                    for (int i = 0; i < num; i++) {
                        str+= "\n";
                         //输出数字前的空格，每行输出的空格数量为：num-1-i
                        for (int j = i; j < num - 1; j++) {
                            //System.out.print(" ");
                            str+= "  ";
                        }
                        // 开始输出具体的数字以及数字之间的空格
                        for (int j = 0; j < i + 1; j++) {
                            //System.out.print(a[i][j] + " ");
                            str+= a[i][j] + "  ";
                        }
                        System.out.println();
                    }
                }
                end.setText(str);
                str="";
            }

        });

        start2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String s = mynum.getText().toString();
                int num = Integer.parseInt(s);
                int i = testFibonacci3(num);

                end.setText(i+"");
                str="";
            }
        });
        start3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String s = mynum.getText().toString();
                int num = Integer.parseInt(s);

                long factorial = factorial(num);

                end.setText(factorial+"");
                str="";
            }
        });

    }
//斐波那契
    public static int testFibonacci3(int n) {
        if (n == 1 || n == 2) {
            return 1;
        }else {
            return testFibonacci3(n-1) + testFibonacci3(n-2);
        }
    }
//递归阶乘
    public int factorial(int m)
    {
        if (m < 0) {
            return 0;
        }
        else if ( m == 1){
            return 1;
        }
        else if (m > 1) {
            return m * factorial(m - 1);
        }
        return 0;
    }


}