HDU-3068 最长回文串

来源：互联网发布：管家婆软件怎么样编辑：程序博客网时间：2024/05/16 08:53

用的Manacher法，O(n)复杂度，证明跟kmp算法一样说不清
代码基本上是参考博客链接
dp法内存不够，中心扩展法时间不够

//Manacher法#include <cstdio>#include <cstring>#include <vector>#include <queue>#include <iostream>#include <cmath>#include <vector>#include <algorithm>#include <map>#include <set>using namespace std;typedef long long ll;#define DEBUGconst int maxn=110000*2+5,maxv=26,INF=0x3f3f3f3f,mod=100000000;char str[maxn],s[maxn];int rad[maxn];int main(){#ifdef DEBUG    freopen("in.txt", "r", stdin);    freopen("out.txt", "w", stdout);#endif    while(cin>>str){        int len=strlen(str);        int ans=0;        memset(rad,0,sizeof(rad));        for(int i=0;i<len;i++){            s[2*i]='#',s[2*i+1]=str[i];        }        s[2*len]='#';s[2*len+1]='\0';        int n=strlen(s);        for(int i=1,j=0,k;i<n;i+=k){            while(s[i-j-1]==s[i+j+1]&&i+j+1<n)j++;            rad[i]=j;            for(k=1;k<=j&&rad[i-k]+k!=rad[i];k++){                rad[i+k]=min(rad[i-k],rad[i]-k);            }            j=max(j-k,0);        }        for(int i=0;i<n;i++){            // printf("%d ", rad[i]);            ans=max(ans,rad[i]);        }        printf("%d\n",ans);    }#ifdef DEBUG    fclose(stdin);    fclose(stdout);#endif    return 0;}

//中心扩展法#include <cstdio>#include <cstring>#include <vector>#include <queue>#include <iostream>#include <cmath>#include <vector>#include <algorithm>#include <map>#include <set>using namespace std;typedef long long ll;#define DEBUGconst int maxn=110000+5,maxv=26,INF=0x3f3f3f3f,mod=100000000;char str[maxn];int main(){#ifdef DEBUG    freopen("in.txt", "r", stdin);    freopen("out.txt", "w", stdout);#endif    while(cin>>str){        int n=strlen(str);        int ans=1;        for(int i=0;i<n;i++){            int j=i,k=i;            while(j>=0&&k<n){                j--;k++;                if(str[j]==str[k]){                    ans=max(ans,k-j+1);                }            }        }        for(int i=0;i<n-1;i++){            int j=i,k=i+1;            while(j>=0&&k<n){                if(str[j]==str[k]){                    ans=max(ans,k-j+1);                }                j--;k++;            }        }        printf("%d\n",ans);    }#ifdef DEBUG    fclose(stdin);    fclose(stdout);#endif    return 0;}

//dp法，内存开不了那么大#include <cstdio>#include <cstring>#include <vector>#include <queue>#include <iostream>#include <cmath>#include <vector>#include <algorithm>#include <map>#include <set>using namespace std;typedef long long ll;#define DEBUGconst int maxn=110000+5,maxv=26,INF=0x3f3f3f3f,mod=100000000;int dp[maxn][maxn];char str[maxn];int main(){#ifdef DEBUG    freopen("in.txt", "r", stdin);    freopen("out.txt", "w", stdout);#endif    while(cin>>str){        int n=strlen(str);        int ans=1;        memset(dp,0,sizeof(dp));        for(int i=0;i<n;i++){            if(i&&str[i-1]==str[i])dp[i-1][i]=1,ans=2;            dp[i][i]=1;        }        for(int i=3;i<=n;i++){            for(int j=0;j<n;j++){                if(j+i-1>=n)break;                if(dp[j+1][j+i-2])dp[j][j+i-1]=1,ans=i;            }        }        printf("%d\n",ans);    }#ifdef DEBUG    fclose(stdin);    fclose(stdout);#endif    return 0;}

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