有點像DP的思想，寫寫就會做。

#include<bits/stdc++.h> using namespace std; const int maxn=1e7+5; char a[maxn]; char s[2*maxn]; int len[maxn*2]; int manachar(char *p) {int le=strlen(p);for(int i=0;i<le;i++){s[i*2+2]=p[i];s[i*2+1]='+';//cout<<s[i*2+1]<<s[i*2+2];}s[0]='^',s[le*2+1]='+';//選取不可能出現的字符即可。//預處理字符串成為一個奇數串；int Max=0,pos=0,ans=0;le=2*le+1;for(int i=1;i<=le;i++){if(Max>i){len[i]=min(len[2*pos-i],Max-i);}else len[i]=1;while(s[i-len[i]]==s[i+len[i]])len[i]++;ans =max(len[i],ans);if(i+len[i]>Max){Max=len[i]+i;pos=i;}}return ans-1; } int main() {int cnt=0;while(~scanf(" %s",a)){if(a[0]=='E')break;printf("Case %d: %d\n",++cnt,manachar(a));memset(a,0,sizeof(a));}return 0; } /*..ii7vJJuJ1juJJYL7r::. :71XPKK5IU1JjssLYLJYJJUU5SKSX1Li. .r1KPX2Yv77r7r7r777r7r7r7r7r7r7777sJ25XUJi. :sPPXY7r7r7r77LrvL7r7r7r7r7r7r7r7r7r7r7777vYUSKJr. . :7ISKSX5Ur :1bKu7777r7r7777ULr7us7777777r7r7r7r7r77777r7r77v7s2K27. :vI5K5KSILi rS51v7777vLXg vbqu7777r777777777rrr7r7r777r7r777r777r7r777r7r7r777r77L1qUi .Equvv777v7u2q1i .5577777v77r7iXSvb577r7r7r7r7777777717rLjr7r77777777777r777r777r7r7r7r7r7777L5SLgv77777r7r7777YIXi .qs777vu2j1Jrr2XXYrr7r77777r7r7r77v11JUJ1U1r7r7r77777r7r777r7777777r7r77777r7r7rBvr77r7r777r77777vX2 KY777vIi :dP1ri7r777r777777777rvs. 7r .2r7r7777777r7r7777777r777r77777r7r7rvZrr7rrv22UL777r7r77UK rX77r72. sbrrr7r777r77777r7r7r7ss 7i S7r7r777r77777r77777777777777777r7r77vr7r7u1:::YSJr777777US qv77775 rEuirr7r7r7777777r7r7r7r7sJvUsJsuuvr7r7r7r7r7r77777777777r7r7r7r777r7r7r7777d .1Ur7r777rq7 Evr777L7rPq7r7r777r77777r7rrrrirvju2IXUII5II1u7v77r7rrr7r777r777r7777777r777r7r777r7r7S. 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總結

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