【HDOJ】3068 最长回文

马拉车算法O(n)可解。

 /* 3068 */
 #include <iostream>
 #include <string>
 #include <map>
 #include <queue>
 #include <set>
 #include <stack>
 #include <vector>
 #include <deque>
 #include <algorithm>
 #include <cstdio>
 #include <cmath>
 #include <ctime>
 #include <cstring>
 #include <climits>
 #include <cctype>
 #include <cassert>
 #include <functional>
 using namespace std;
 //#pragma comment(linker,"/STACK:102400000,1024000")

 #define sti                set<int>
 #define stpii            set<pair<int, int> >
 #define mpii            map<int,int>
 #define vi                vector<int>
 #define pii                pair<int,int>
 #define vpii            vector<pair<int,int> >
 #define rep(i, a, n)     for (int i=a;i<n;++i)
 #define per(i, a, n)     for (int i=n-1;i>=a;--i)
 #define clr                clear
 #define pb                 push_back
 #define mp                 make_pair
 #define fir                first
 #define sec                second
 #define all(x)             (x).begin(),(x).end()
 #define SZ(x)             ((int)(x).size())
 #define lson            l, mid, rt<<1
 #define rson            mid+1, r, rt<<1|1

 const int maxn = ;
 char s[maxn*], ss[maxn];
 int P[maxn*];
 int ans, l;

 void init() {
     int i, len = strlen(ss);

     l = ;
     s[l++] = '@';
     s[l++] = '#';
     for (i=; i<len; ++i) {
         s[l++] = ss[i];
         s[l++] = '#';
     }
     s[l++] = '\0';
 }

 void manacher() {
     int i, mx = , id;

     for (i=; i<l; ++i) {
         P[i] = mx>i ? min(P[*id-i], mx-i) : ;
         while (s[i+P[i]] == s[i-P[i]])
             ++P[i];
         if (i+P[i] > mx) {
             mx = i + P[i];
             id = i;
         }
     }

     ans = ;
     for (i=; i<l; ++i)
         ans = max(ans, P[i]);
     printf("%d\n", ans-);
 }

 void solve() {
     init();
     manacher();
 }

 int main() {
     ios::sync_with_stdio(false);
     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     while (scanf("%s", ss)!=EOF) {
         solve();
     }

     #ifndef ONLINE_JUDGE
         printf("time = %d.\n", (int)clock());
     #endif

     return ;
 }