【HDOJ】4513 吉哥系列故事——完美队形II

这题目上学期就看了，不过最近发现可以用马拉车来解，而且还是基本算法。 稍微对回文串成立条件变形一下即可。

/* 4513 */
#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>
#include <iterator>
#include <iomanip>
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 = 1e5+5;
int a[maxn], b[maxn*2];
int Len[maxn*2];

void init(int n) {
    int j = 0;
    
    b[j++] = -1;
    b[j++] = 0;
    rep(i, 0, n) {
        b[j++] = a[i];
        b[j++] = 0;
    }
}

void manacher(int m) {
    int n = 2*m+1;
    int p = 0, p0 = 0;
    int lid, rid;
    
    rep(i, 1, n+1) {
        if (p > i)
            Len[i] = min(p-i, Len[2*p0-i]);
        else
            Len[i] = 1;
        
        while (b[i+Len[i]] == b[i-Len[i]]) {
            if (b[i+Len[i]] > 0) {
                lid = i - Len[i];
                rid = i + Len[i];
                if (b[lid]>b[lid+2] || b[rid]>b[rid-2])
                    break;
            }
            ++Len[i];
        }
        
        if (i+Len[i] > p) {
            p = i + Len[i];
            p0 = i;
        }
    }
}

void solve(int n) {
    init(n);
    manacher(n);
    
    int ans = 0;
    
    n = n*2+1;
    rep(i, 1, n) {
        ans = max(ans, Len[i]);
    }
    printf("%d
", ans-1);
}

int main() {
    ios::sync_with_stdio(false);
    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        freopen("data.out", "w", stdout);
    #endif
    
    int t;
    int n;
    
    scanf("%d", &t);
    while (t--) {
        scanf("%d", &n);
        rep(i, 0, n)
            scanf("%d", &a[i]);
        solve(n);
    }
    
    #ifndef ONLINE_JUDGE
        printf("time = %d.
", (int)clock());
    #endif
    
    return 0;
}