解析

本题解是用KMP算法来完成此题。

Code

#include <bits/stdc++.h>
#define N 1000005
#define ll long long
using namespace std;

int k[N];
string s;
ll len, ans; 

ll f (ll x)
{
	if (k[x] != 0) return k[x] = f (k[x]);
	return x; 
}

int main ()
{
	cin >> len >> s;
	s = ' ' + s;
	k[1] = 0;
	ll i = 1, j = 0;
	while (i < len)
	{
		while (j && s[j + 1] != s[i + 1]) j = k[j];
		if (s[j + 1] == s[i + 1]) ++ j;
		k[i + 1] = j;
		++ i;
	}
	for (i = 1; i <= len; ++ i) ans += i - f (i);
	printf ("%lld", ans);
	return 0;
}