Luogu3435 [POI2006]OKR-Periods of Words （KMP）

\(next\)应用，将原串视作最长前缀复制后的子串

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int  a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int  a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Abs(a) ((a) < 0 ? -(a) : (a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long

#define ON_DEBUG

#ifdef ON_DEBUG

#define D_e_Line printf("\n\n----------\n\n")
#define D_e(x)  cout << #x << " = " << x << endl
#define Pause() system("pause")
#define FileOpen() freopen("in.txt","r",stdin);

#else

#define D_e_Line ;
#define D_e(x)  ;
#define Pause() ;
#define FileOpen() ;

#endif

struct ios{
    template<typename ATP>ios& operator >> (ATP &x){
        x = 0; int f = 1; char c;
        for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-')  f = -1;
        while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
        x*= f;
        return *this;
    }
}io;
using namespace std;

int nxt[1000007];
char str[1000007];
int main(){
	int len;
	io >> len;
	scanf("%s", str);
	long long ans = 0;
	int i = 0, j = -1;
	nxt[0] = -1;
	while(i < len){
		if(j == -1 || str[i] == str[j]){
			nxt[++i] = ++j;
			while(nxt[nxt[i]] > 0) nxt[i] = nxt[nxt[i]];
			if(nxt[i] > 0){
				ans += i -nxt[i];
			}
		}
		else
			j = nxt[j];
	}

	printf("%lld", ans);
	return 0;
}