UVA-11536 Smallest Sub-Array

题目大意：给出一个有n个数的序列，找出最短的涵盖1~k之间所有整数的连续区间。

题目分析：扫描一遍序列，维护head、tail两个位置。要注意，最短的区间上两端的数一定[1,k]上。

 

代码如下：

# include<iostream>
# include<cstdio>
# include<cstring>
# include<algorithm>
using namespace std;const int INF=1<<30;
int n,m,k,a[1000005],mark[1005];bool ok()
{for(int i=1;i<=k;++i)if(!mark[i])return false;return true;
}int solve()
{if(k<=3)return k;memset(mark,0,sizeof(mark));int head=0,tail,ans=INF;a[0]=1,a[1]=2,a[2]=3;mark[1]=mark[2]=mark[3]=1;for(tail=3;tail<n;++tail){a[tail]=(a[tail-1]+a[tail-2]+a[tail-3])%m+1;++mark[a[tail]];while(head<=tail&&(a[head]<1||a[head]>k||mark[a[head]]>1))--mark[a[head++]];if(tail-head+1>=k&&tail-head+1<ans&&ok())ans=tail-head+1;}return ans;
}int main()
{int T,cas=0;scanf("%d",&T);while(T--){scanf("%d%d%d",&n,&m,&k);printf("Case %d: ",++cas);if(n<k||k>m){printf("sequence nai\n");continue;}int ans=solve();if(ans==INF)printf("sequence nai\n");elseprintf("%d\n",ans);}return 0;
}