using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Program.ave(5, 10));

        Console.WriteLine(Program.sumEvenFor(11));

        Console.WriteLine(Program.sumEvenIf(5, 11));

        Program.printArr(Program.swapArr(new int[] {1, 2, 3, 4, 5}));

        Console.WriteLine(Program.distance(new int[] {1, 2, 3, 4, 5}));

        Program.printMatrix(Program.zeroMatrix(new int[][] {

            new int[] {1, 2, 3, 4},

            new int[] {5, 6, 7, 8},

            new int[] {9, 10, 11, 12},

            new int[] {13, 14, 15, 16},

        }));

    }

    // 1.a

    public static int ave(int n, int m) {

        int s = 0;

        for (int i = n; i <= m; i++) {

            s += i;

        }

        return s;

    }

    // 1b

    public static int sumEvenFor(int n1) {

        int s = 0;

        for (int i = 0; i <= n1; i += 2) {

            s += i;

        }

        return s;

    }

​

    // 1c

    public static int sumEvenIf(int n1, int n2) {

        int s = 0;

        int i = n1;

        while (i <= n2) {

            if (i % 2 == 0) {

                s += i;

            }

            i++;

        }

        return s;

    }

​

    //2a

    public static int[] swapArr(int[] arr) {

        int len = arr.Length;

        int buf;

        for (int i = 0; i < len / 2; i++) {

            buf = arr[i];

            arr[i] = arr[len - i - 1];

            arr[len - i - 1] = buf;

        }

        return arr;

    }

    private static void printArr(int[] arr) {

        for (int i = 0; i < arr.Length; i++) {

            Console.WriteLine(arr[i]);

        }

    }

    // 2b

    public static int distance(int[] arr) {

        int len = arr.Length;

        int max = arr[0];

        int first = 0;

        int last;

        for (int i = 1; i < len; i++) {

            if (arr[i] > max) {

                max = arr[i];

                first = i;

            }

        }

        last = first;

        for (int i = len - 1; i > first; i--) {

            if (arr[i] == max) {

                last = i;

                break;

            }

        }

        return last - first;

    }

    // 3

    public static int[][] zeroMatrix(int[][] matrix) {

        int len = matrix.Length; // it's a matrix so it has identical width and height

        for (int y = 0; y < len; y++) {

            for (int x = 0; x < len; x++) {

                if (y > x) {

                    matrix[y][x] = 0;

                }

            }

        }

        return matrix;

    }

    private static void printMatrix(int[][] matrix) {

        int len = matrix.Length;

        for (int y = 0; y < len; y++) {

            for (int x = 0; x < len; x++) {

                Console.Write(matrix[y][x].ToString() + ' ');

            }

            Console.WriteLine();

        }

    }

}