51nod 1286 三段子串（树状数组+拓展kmp）

#include <iostream>
#include <cstring>
#include <vector>
using namespace std;
const int maxn = 1e6 + 100;
char S[maxn];
int Next[maxn], extend[maxn];
vector<int> G[maxn];
int len;
int c[maxn*4];
void Modify(int x, int s){
    for(; x <= len; x += x&(-x)) c[x] += s;
}
int Query(int y){
    if(y <= 0) return 0;
    int ans = 0;
    for(int x = y; x; x -= x&(-x)) ans += c[x];
    return ans;
}
int query(int x, int y) { return x <= y ? Query(y) - Query(x-1) : 0; }
void GetNext(char *T, int *Next){
    int len = strlen(T);
    Next[0] = len;
    int a, p;
    for(int i = 1, j = -1; i < len; i++, j--){
       if(j < 0 || i + Next[i-a] >= p){
            if(j < 0) p = i, j = 0;
            while(p < len && T[p] == T[j])
                p++, j++;
            Next[i] = j;
            a = i;
       } else Next[i] = Next[i-a];
    }
}
void GetExtend(char *S, char *T, int *extend, int *Next){
    GetNext(T, Next);
    int a, p;
    int slen = strlen(S), tlen = strlen(T);
    for(int i = 0, j = -1; i < slen; i++, j--){
        if(j < 0 || i + Next[i-a] >= p){
            if(j < 0) p = i, j = 0;
            while(p < slen && j < tlen && S[p] == T[j]) p++, j++;
            extend[i] = j;
            a = i;
        } else extend[i] = Next[i-a];
    }
}

int main()
{
    cin>>S;
    len = strlen(S);
    GetNext(S, Next);
    //for(int i = 0; i < len; i++) cout<<Next[i]<<" "; cout<<endl;
    for(int i = 0; i < len; i++) G[Next[i]].push_back(i);
    int ans = 0;
    for(int i = len-1; i >= 1; i--){
        for(auto x : G[i]) Modify(x+1, 1);
        int n = G[i].size();
        if(n == 0) continue;
        if(G[i][n-1] != len-i) continue;
        if(query(i+1, len-2*i+1)) { ans = i; break; }
    }
    cout<<ans<<endl;
    return 0;
}