HDU 4513 吉哥系列故事――完美队形II （manacher算法）

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <set>
using namespace std;

const int maxn = 1e5 + 7;
int n;
int s[maxn];
int ss[maxn<<1];
int p[maxn<<1];

void make() {
    ss[0] = -1;
    int pos = 0;
    for(int i = 0; i < n; i++) {
        ss[++pos] = 0;
        ss[++pos] = s[i];
    }ss[++pos] = 0;
    n = n * 2 + 2;
    //for(int i = 0; i < n; i++) printf("%d ", ss[i]); puts("");
}

void solve() {
    int maxx = 0, id;
    for(int i = 1; i < n; i++) {
        if(maxx > i)
            p[i] = min(p[id * 2 -  i], p[id] + id - i);
        else p[i] = 1;
        int Min;
        if(ss[i] > 0) Min = ss[i];
        else Min = ss[i + 1];
        while(ss[i - p[i]] == ss[i + p[i]] && ss[i - p[i]] <= Min) {
            //printf("are you here?\n");
            if(ss[i - p[i]] > 0)
                Min = ss[i - p[i]];
            if(i + p[i] > maxx) {
                maxx = i + p[i];
                id = i;
            }
            p[i]++;
        }
    }
    int ans = 0;
    for(int i = 1; i < n; i++) ans = max(ans, p[i]);
    printf("%d\n", ans - 1);
}

int main() {
    int t;
    scanf("%d", &t);
    while(t--) {
        scanf("%d", &n);
        for(int i = 0; i < n; i++) {
            scanf("%d", &s[i]);
        }
        make();
        solve();
    }
}