1 # include <stdio.h>
2
3 int search(int a[], int n, int v) //这个好像是效率最高的
4 {
5 int left = -1, right = n, middle;
6 while(left+1 != right)
7 {
8 middle = left + (right-left) / 2;
9 if(a[middle] < v)
10 left = middle;
11 else
12 right = middle;
13 }
14 if(right >= n || a[right] != v)
15 right = -1;
16 return right;
17 }
18
19 int search1(int a[], int n, int v)
20 {
21 int left = 0, right = n-1, middle;
22 while(left <= right)
23 {
24 middle = (left+right) / 2;
25 if(a[middle] > v)
26 right = middle - 1;
27 else if(a[middle] < v)
28 left = middle +1;
29 else
30 return middle;
31 }
32 return -1;
33 }
34
35 int search2(int a[], int n, int v)
36 {
37 int left = 0, right = n, middle;
38 while(left < right)
39 {
40 middle = (right + left) / 2;
41 if(a[middle] > v)
42 right = middle;
43 else if(a[middle] < v)
44 left = middle + 1;
45 else
46 return middle;
47 }
48 return -1;
49 }
50
51 int a[1000000];
52 int main(void)
53 {
54 int n, i, t, ans;
55 while(~scanf("%d", &n))
56 {
57 for(i = 0; i < n; i++)
58 scanf("%d", &a[i]);
59 scanf("%d", &t);
60 ans = search(a, n, t);
61 if(ans <= 0)
62 printf("NO\n");
63 else
64 printf("YES\n");
65 }
66
67 return 0;
68 }
