Codeforces 339E

 1 #include <cstdio>
 2 #include <algorithm>
 3 #include <cmath>
 4 #include <cstring>
 5 #include <cstdlib>
 6 #include <ctime>
 7 #include <set>
 8 #include <map>
 9 using namespace std;
10 
11 const int maxn=1100;
12 
13 struct point
14 {
15     int x, y;
16 };
17 
18 int n;
19 int sum;
20 int a[maxn], des[maxn];
21 point ans[10];
22 
23 void init()
24 {
25     scanf("%d", &n);
26     a[0]=0; a[n+1]=n+1;
27     for (int i=1; i<=n; ++i) scanf("%d", &a[i]);
28 }
29 void rev(int le, int ri)
30 {
31     for (int i=le; i<=(ri+le)/2; ++i)
32         swap(a[i], a[ri-(i-le)]);
33 }
34 bool check()
35 {
36     for (int i=1; i<=n; ++i)
37         if (a[i]!=i) return false;
38     return true;
39 }
40 void print(int step)
41 {
42     printf("%d\n", step);
43     for (int i=step; i>0; --i)
44         printf("%d %d\n", ans[i].x, ans[i].y);
45     exit(0);
46 }
47 void dfs(int k)
48 {
49     if (check()) print(k-1);
50     if (k>3) return;
51     for (int i=1; i<n; ++i)
52         for (int j=i+1; j<=n; ++j)
53             if (abs(a[i-1]-a[j])==1 || abs(a[i]-a[j+1])==1)
54             {
55                 ans[k].x=i;
56                 ans[k].y=j;
57                 rev(i, j);
58                 dfs(k+1);
59                 rev(i, j);
60             }
61 }
62 int main()
63 {
64     freopen("input.txt", "r", stdin);
65     freopen("output.txt", "w", stdout);
66     init();
67     dfs(1);
68     return 0;
69 }