【迴文串】ural 1297

迴文串，原理：由一點向兩邊延伸，注意不要超出數組範圍！聽說可以用尾碼數組，不懂，有空再研究研究

#include <vector>#include <list>#include <map>#include <set>#include <queue>#include <string.h>#include <deque>#include <stack>#include <bitset>#include <algorithm>#include <functional>#include <numeric>#include <utility>#include <sstream>#include <iostream>#include <iomanip>#include <cstdio>#include <cmath>#include <cstdlib>#include <limits.h>using namespace std;int lowbit(int t){return t&(-t);}int countbit(int t){return (t==0)?0:(1+countbit(t&(t-1)));}int gcd(int a,int b){return (b==0)?a:gcd(b,a%b);}#define LL long long#define PI acos(-1.0)#define N  100001#define MAX INT_MAX#define MIN INT_MIN#define eps 1e-8#define FRE freopen("a.txt","r",stdin)char str[N];int st,en;int len;int maxlen;void gao(int s,int t){    while(s>0 && t<len-1){        if(str[s-1]!=str[t+1])break; // !!!!這裡要注意不能寫成str[s]!=str[t]            s--;            t++;    }    if(t-s+1>maxlen){        st=s;        en=t;        maxlen=t-s+1;    }}int main(){    while(scanf("%s",str)!=EOF){        int i,j,k;        len=strlen(str);        maxlen=0;        for(i=0;i<len;i++)gao(i,i);        for(i=1;i<len;i++)        if(str[i-1]==str[i])        gao(i-1,i);        for(i=st;i<=en;i++)        printf("%c",str[i]);        puts("");    }    return 0;}