DP Codeforces Round #FF (Div. 1) A. DZY Loves Sequences

题目传送门

 /*
      DP：先用l，r数组记录前缀后缀上升长度，最大值会在三种情况中产生：
         1. a[i-1] + 1 < a[i+1]，可以改a[i]，那么值为l[i-1] + r[i+1] + 1
         2. l[i-1] + 1   3. r[i+1] + 1   //修改a[i]
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 using namespace std;

 const int MAXN = 1e5 + ;
 const int INF = 0x3f3f3f3f;
 int a[MAXN];
 int l[MAXN], r[MAXN];
 int n;

 int main(void)      //Codeforces Round #FF (Div. 1) A. DZY Loves Sequences
 {
     scanf ("%d", &n);    int ans = ;
     for (int i=; i<=n; ++i)
     {
         scanf ("%d", &a[i]);
         l[i] = ;
         if (i >  && a[i] > a[i-])    l[i] = l[i-] + ;
     }

     for (int i=n; i>=; --i)
     {
         r[i] = ;
         if (i < n && a[i] < a[i+])    r[i] = r[i+] + ;
     }

     for (int i=; i<=n; ++i)
     {
         ans = max (ans, l[i]);    ans = max (ans, r[i]);
         if (i >  && i < n && a[i-] +  < a[i+])    ans = max (ans, l[i-] + r[i+] + );
         if (i > )    ans = max (ans, l[i-] + );
         if (i < n)    ans = max (ans, r[i+] + );
     }

     printf ("%d\n", ans);

     return ;
 }