Task: Display a linear combination
C#: using System;
using System.Collections.Generic;
using System.Text;

namespace DisplayLinearCombination {
    class Program {
        static string LinearCombo(List<int> c) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < c.Count; i++) {
                int n = c[i];
                if (n < 0) {
                    if (sb.Length == 0) {
                        sb.Append('-');
                    } else {
                        sb.Append(" - ");
                    }
                } else if (n > 0) {
                    if (sb.Length != 0) {
                        sb.Append(" + ");
                    }
                } else {
                    continue;
                }

                int av = Math.Abs(n);
                if (av != 1) {
                    sb.AppendFormat("{0}*", av);
                }
                sb.AppendFormat("e({0})", i + 1);
            }
            if (sb.Length == 0) {
                sb.Append('0');
            }
            return sb.ToString();
        }

        static void Main(string[] args) {
            List<List<int>> combos = new List<List<int>>{
                new List<int> { 1, 2, 3},
                new List<int> { 0, 1, 2, 3},
                new List<int> { 1, 0, 3, 4},
                new List<int> { 1, 2, 0},
                new List<int> { 0, 0, 0},
                new List<int> { 0},
                new List<int> { 1, 1, 1},
                new List<int> { -1, -1, -1},
                new List<int> { -1, -2, 0, -3},
                new List<int> { -1},
            };

            foreach (List<int> c in combos) {
                var arr = "[" + string.Join(", ", c) + "]";
                Console.WriteLine("{0,15} -> {1}", arr, LinearCombo(c));
            }
        }
    }
}

Java: import java.util.Arrays;

public class LinearCombination {
    private static String linearCombo(int[] c) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < c.length; ++i) {
            if (c[i] == 0) continue;
            String op;
            if (c[i] < 0 && sb.length() == 0) {
                op = "-";
            } else if (c[i] < 0) {
                op = " - ";
            } else if (c[i] > 0 && sb.length() == 0) {
                op = "";
            } else {
                op = " + ";
            }
            int av = Math.abs(c[i]);
            String coeff = av == 1 ? "" : "" + av + "*";
            sb.append(op).append(coeff).append("e(").append(i + 1).append(')');
        }
        if (sb.length() == 0) {
            return "0";
        }
        return sb.toString();
    }

    public static void main(String[] args) {
        int[][] combos = new int[][]{
            new int[]{1, 2, 3},
            new int[]{0, 1, 2, 3},
            new int[]{1, 0, 3, 4},
            new int[]{1, 2, 0},
            new int[]{0, 0, 0},
            new int[]{0},
            new int[]{1, 1, 1},
            new int[]{-1, -1, -1},
            new int[]{-1, -2, 0, -3},
            new int[]{-1},
        };
        for (int[] c : combos) {
            System.out.printf("%-15s  ->  %s\n", Arrays.toString(c), linearCombo(c));
        }
    }
}