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

 

题目传送门

 1 /*  2  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：  3  1. a[i-1] + 1 < a[i+1]，可以改a[i]，那么值为l[i-1] + r[i+1] + 1  4  2. l[i-1] + 1 3. r[i+1] + 1 //修改a[i]  5 */  6 #include <cstdio>  7 #include <algorithm>  8 #include <cstring>  9 using namespace std; 10 11 const int MAXN = 1e5 + 10; 12 const int INF = 0x3f3f3f3f; 13 int a[MAXN]; 14 int l[MAXN], r[MAXN]; 15 int n; 16 17 int main(void) //Codeforces Round #FF (Div. 1) A. DZY Loves Sequences 18 { 19 scanf ("%d", &n); int ans = 0; 20 for (int i=1; i<=n; ++i) 21  { 22 scanf ("%d", &a[i]); 23 l[i] = 1; 24 if (i > 1 && a[i] > a[i-1]) l[i] = l[i-1] + 1; 25  } 26 27 for (int i=n; i>=1; --i) 28  { 29 r[i] = 1; 30 if (i < n && a[i] < a[i+1]) r[i] = r[i+1] + 1; 31  } 32 33 for (int i=1; i<=n; ++i) 34  { 35 ans = max (ans, l[i]); ans = max (ans, r[i]); 36 if (i > 1 && i < n && a[i-1] + 1 < a[i+1]) ans = max (ans, l[i-1] + r[i+1] + 1); 37 if (i > 1) ans = max (ans, l[i-1] + 1); 38 if (i < n) ans = max (ans, r[i+1] + 1); 39  } 40 41 printf ("%d\n", ans); 42 43 return 0; 44 }