CodeForces 447C DZY Loves Sequences DP

题目：click here

题意：求给定序列更改其中一个元素后的最长连续上升子序列的长度

分析：最长的连续子序列有2种，一种是严格上升(没有更改元素)的长度加1，一种是两段严格上升的加起来。

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 #define F first
 4 #define S second
 5 #define pb push_back
 6 #define power(a) ((a)*(a))
 7 #define ENTER printf("\n");
 8 typedef unsigned long long ll;
 9 const int INF = 0x3f3f3f3f;
10 const double EPS = 1e-8;
11 const int M = 1e5+5;
12
13 int n, ret;
14 int a[M];
15 int dps[M];     // dps[i]保存以i开头的最长连续上升子序列
16 int dpe[M];     // dpe[i]保存以i结束的最长连续上升子序列
17 void solve()    {
18     ret = dpe[0] = dps[n-1] = 1;
19     for( int i=1; i<n; i++ )
20         if( a[i] > a[i-1] ) dpe[i] = dpe[i-1] + 1;
21         else dpe[i] = 1;
22     for( int i=n-2; i>=0; i-- )
23         if( a[i] < a[i+1] ) dps[i] = dps[i+1] + 1;
24         else dps[i] = 1;
25     for( int i=0; i<n; i++ )
26         if( a[i+1]-a[i-1] >= 2 ) ret = max( ret, dps[i+1]+dpe[i-1]+1 );
27         else ret = max( ret, max( dps[i+1]+1, dpe[i-1]+1 ) );
28     printf("%d\n", ret);
29 }
30
31 int main()  {
32     while( ~scanf("%d", &n ) )  {
33         for( int i=0; i<n; i++ )
34             scanf("%d", a+i);
35         solve();
36     }
37     return 0;
38 }

转载于:https://www.cnblogs.com/TaoTaoCome/p/4744539.html

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