1 /// <summary>
2 /// Solution A
3 /// 100/100
4 /// </summary>
5 /// <param name="A"></param>
6 /// <returns></returns>
7 public static int solution(int[] A)
8 {
9 HashSet<int> hs = new HashSet<int>();
10
11 foreach (int i in A)
12 {
13 hs.Add(i);
14 }
15
16 for (int i = 1; i <= A.Length + 1; i++)
17 {
18 if (!hs.Contains(i))
19 return i;
20 }
21 return 0;
22 }
23
24 /// <summary>
25 /// Solution B
26 /// 100/100
27 /// </summary>
28 /// <param name="A"></param>
29 /// <returns></returns>
30 public static int solution(int[] A)
31 {
32
33 //int N = A.Length;
34 long N = A.Length;
35
36 //总和可能超出int最大值，所以用long
37 long sumFull = (N + 1) * (N + 2) / 2;
38
39 //long sumLack = A.Sum();
40 long sumLack = 0;
41
42 foreach (int i in A)
43 sumLack += i;
44
45 return (int)(sumFull - sumLack);
46 }
47
48 /// <summary>
49 /// Solution C
50 /// 100/100
51 /// </summary>
52 /// <param name="A"></param>
53 /// <returns></returns>
54 public static int solution(int[] A)
55 {
56 Array.Sort(A);
57 int N = A.Length;
58 for (int i = 1; i <= N; i++)
59 {
60 if (A[i - 1] != i)
61 return i;
62 }
63 return N + 1;
64 }
