hdu 4745

直接在圈上写类似与lcs的dp就可以了

悲剧的是 （j+1）% n 直接写成了 j+1，死都找不到错

#pragma comment(linker, "/STACK:102400000,102400000")#include<iostream>#include<vector>#include<algorithm>#include<cstdio>#include<queue>#include<stack>#include<string>#include<map>#include<set>#include<cmath>#include<cassert>#include<cstring>#include<iomanip>using namespace std;#ifdef _WIN32#define i64 __int64#define out64 "%I64d\n"#define in64 "%I64d"#else#define i64 long long#define out64 "%lld\n"#define in64 "%lld"#endif/************ for topcoder by zz1215 *******************/#define foreach(c,itr)  for(__typeof((c).begin()) itr=(c).begin();itr!=(c).end();itr++)#define FOR(i,a,b)      for( int i = (a) ; i <= (b) ; i ++)#define FF(i,a)         for( int i = 0 ; i < (a) ; i ++)#define FFD(i,a,b)      for( int i = (a) ; i >= (b) ; i --)#define S64(a)          scanf(in64,&a)#define SS(a)           scanf("%d",&a)#define LL(a)           ((a)<<1)#define RR(a)           (((a)<<1)+1)#define pb              push_back#define pf              push_front#define X               first#define Y               second#define CL(Q)           while(!Q.empty())Q.pop()#define MM(name,what)   memset(name,what,sizeof(name))#define MC(a,b)         memcpy(a,b,sizeof(b))#define MAX(a,b)        ((a)>(b)?(a):(b))#define MIN(a,b)        ((a)<(b)?(a):(b))#define read            freopen("in.txt","r",stdin)#define write           freopen("out.txt","w",stdout)const int inf = 0x3f3f3f3f;const i64 inf64 = 0x3f3f3f3f3f3f3f3fLL;const double oo = 10e9;const double eps = 10e-9;const double pi = acos(-1.0);const int maxn = 1111;int n;int s[maxn];int dp[maxn][maxn];int start(){for(int i=0;i<n;i++){for(int j=0;j<n;j++){dp[i][j] = 0;}}for(int i=0;i<n;i++){dp[i][i] = 1;}for(int j=0;j<n;j++){if(s[j] == s[(j+1)%n]){dp[j][(j+1)%n] = 2;}else{dp[j][(j+1)%n] = 1;}}for(int i=2;i<n;i++){for(int j=0;j<n;j++){if(s[j] == s[(j+i)%n] ){dp[j][(j+i)%n] = dp[(j+1)%n][(j+i-1+n)%n] + 2;}else{dp[j][(j+i)%n] = max(dp[(j+1)%n][(j+i)%n],dp[j][(j+i-1+n)%n]);  //好吧，就是这写错了}}}int ans = 0;for(int i=0;i<n;i++){ans = max(ans,dp[i][(i+n-2)%n]+1);ans = max(ans,dp[i][(i+n-1)%n]);}return ans;}int main(){while(cin>>n){if(n == 0) return 0;for(int i=0;i<n;i++){SS(s[i]);}if(n==1) cout<<1<<endl;else cout<<start()<<endl;}return 0;}