1055 最长等差数列

 1 #include<stdio.h>
 2 #include<stdlib.h>
 3 #include<iostream>
 4 #include<queue>
 5 #include<math.h>
 6 #include<string.h>
 7 #include<algorithm>
 8 using namespace std;
 9 typedef long long LL;
10 short int dp[10005][10005];
11 LL ans[10005];
12 using namespace std;
13 int main(void)
14 {
15     int i,j;
16     for(i = 0; i <= 10000; i++)
17     {
18         fill(dp[i],dp[i]+10001,2);
19     }
20     int n;
21     scanf("%d",&n);
22     for(i = 1; i <= n; i++)
23     {
24         scanf("%lld",&ans[i]);
25     }
26     sort(ans+1,ans+n+1);
27     int l ,r;short int an = 2;//printf("%d\n",n);
28     for(i = n-1; i >= 1 ; i--)
29     {
30        l = i-1;r = i+1;
31        while(l >= 1&&r <= n)
32        {
33            if(ans[l] + ans[r] ==(LL)2*ans[i])
34            {
35                dp[l][i] = dp[i][r] + 1;
36                an = max(an,dp[l][i]);
37                l--;
38            }
39            else if(ans[l] + ans[r] < (LL)2*ans[i])
40            {
41                r++;
42            }
43            else l--;
44            //printf("%d\n",dp[l][i]);
45        }
46     }
47     printf("%d\n",an);
48     return 0;
49 }