點擊打開鏈接鏈接
Revenge of LIS II
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 1028 Accepted Submission(s): 334
---Wikipedia
Today, LIS takes revenge on you, again. You mission is not calculating the length of longest increasing subsequence, but the length of the second longest increasing subsequence.
Two subsequence is different if and only they have different length, or have at least one different element index in the same place. And second longest increasing subsequence of sequence S indicates the second largest one while sorting all the increasing subsequences of S by its length.
Each test case begins with an integer N, indicating the length of the sequence. Then N integer Ai follows, indicating the sequence.
[Technical Specification]
1. 1 <= T <= 100
2. 2 <= N <= 1000
3. 1 <= Ai <= 1 000 000 000
普通lcs再sort是不對的
反例 :
1 1 2
方法一:
統計到每個長度的個數
#include<cstdio>
#include<cstring>
int max(int a,int b)
{
return a>b?a:b;
}
long long cnt[1111];
int a[1111],dp[1111];
int main()
{
int t,n;
scanf("%d",&t);
while(t--)
{
scanf("%d",&n);
for(int i=1;i<=n;i++)
scanf("%d",&a[i]);
for(int i=1;i<=n;i++)
cnt[i]=1;
int ans=0;
long long num=0;
for(int i=1;i<=n;i++)
{
cnt[i]=1;
dp[i]=1;
for(int j=1;j<i;j++)
{
if(a[j]<a[i])
{
if(dp[i]<dp[j]+1)
{
dp[i]=dp[j]+1;
cnt[i]=cnt[j];
}
else if(dp[i]==dp[j]+1)
cnt[i]+=cnt[j];
}
}
ans=max(ans,dp[i]);
}
for(int i=1;i<=n;i++)
{
if(dp[i]==ans)
num+=cnt[i];
}
if(num==1)
printf("%d\n",ans-1);
else if(num>1)
printf("%d\n",ans);
}
return 0;
}
方法二:
求lcs的第K優解 開二維的dp
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int dp[1111][3];
int a[1111];
int ans[2222];
int main()
{
int t,n;
int s[10];
scanf("%d",&t);
while(t--)
{
scanf("%d",&n);
for(int i=1;i<=n;i++)
scanf("%d",&a[i]);
memset(dp,0,sizeof(dp));
int xx=0;
for(int i=1;i<=n;i++)
{
dp[i][0]=1;
dp[i][1]=0;
for(int j=1;j<i;j++)
{
if(a[j]<a[i])
{
s[0]=dp[j][0]+1;
s[1]=dp[j][1]+1;
s[2]=dp[i][0];
s[3]=dp[i][1];
sort(s,s+4);
dp[i][0]=s[3];
dp[i][1]=s[2];
}
}
ans[xx++]=dp[i][0];
ans[xx++]=dp[i][1];
}
sort(ans,ans+2*n);
printf("%d\n",ans[xx-2]);
}
return 0;
}