最长上升子序列Lis+最长下降子序列Lds

int LIS(int n)//最长上升子序列
{
    int res = 0;

    for(int i = 0; i < n; ++i)
    {
        dp[i] = 1;
        for(int j = 0; j < i; ++j)
            if(a[j] < a[i]) dp[i] = max(dp[i], dp[j]+1);
        res = max(res, dp[i]);
    }
    return res;
}
int LDS(int n)//最长下降子序列
{
    int res = 0;

    for(int i = 0; i < n; ++i)
    {
        dp[i] = 1;
        for(int j = 0; j < i; ++j)
            if(a[j] > a[i]) dp[i] = max(dp[i], dp[j] + 1);
        res = max(res, dp[i]);
    }
    return res;
}