牛客 CSL的密码

后缀数组

求本质不同的子串，转换为求本质不同的后缀的前缀，每个后缀贡献的前缀数量减去与上一个重复的前缀即为答案。

#include <bits/stdc++.h>
#define INF 0x3f3f3f3f
#define full(a, b) memset(a, b, sizeof a)
#define __fastIn ios::sync_with_stdio(false), cin.tie(0)
#define pb push_back
using namespace std;
using LL = long long;
inline int lowbit(int x){ return x & (-x); }
inline int read(){
    int ret = 0, w = 0; char ch = 0;
    while(!isdigit(ch)){
        w |= ch == '-', ch = getchar();
    }
    while(isdigit(ch)){
        ret = (ret << 3) + (ret << 1) + (ch ^ 48);
        ch = getchar();
    }
    return w ? -ret : ret;
}
template <typename A>
inline A __lcm(A a, A b){ return a / __gcd(a, b) * b; }
template <typename A, typename B, typename C>
inline A fpow(A x, B p, C lyd){
    A ans = 1;
    for(; p; p >>= 1, x = 1LL * x * x % lyd)if(p & 1)ans = 1LL * x * ans % lyd;
    return ans;
}
const int N = 200005;
 
int n, m;
 
namespace SuffixArray{
 
    string s;
    int t[N], t2[N], c[N], sa[N], rank[N], height[N];
 
    void build(int m, int n){
        int *x = t, *y = t2;
        for(int i = 0; i < m; i ++) c[i] = 0;
        for(int i = 0; i < n; i ++) c[x[i] = s[i]] ++;
        for(int i = 1; i < m; i ++) c[i] += c[i - 1];
        for(int i = n - 1; i >= 0; i --) sa[--c[x[i]]] = i;
        for(int k = 1; k <= n; k <<= 1){
            int p = 0;
            for(int i = n - k; i < n; i ++) y[p++] = i;
            for(int i = 0; i < n; i ++){
                if(sa[i] >= k) y[p++] = sa[i] - k;
            }
            for(int i = 0; i < m; i ++) c[i] = 0;
            for(int i = 0; i < n; i ++) c[x[y[i]]] ++;
            for(int i = 1; i < m; i ++) c[i] += c[i - 1];
            for(int i = n - 1; i >= 0; i --) sa[--c[x[y[i]]]] = y[i];
            swap(x, y);
            p = 1, x[sa[0]] = 0;
            for(int i = 1; i < n; i ++){
                x[sa[i]] = y[sa[i - 1]] == y[sa[i]] && sa[i - 1] + k < n && sa[i] + k < n && y[sa[i - 1] + k] == y[sa[i] + k] ? p - 1 : p ++;
            }
            if(p >= n) break;
            m = p;
        }
 
        int k = 0;
        for(int i = 0; i < n; i ++) rank[sa[i]] = i;
        for(int i = 0; i < n; i ++){
            if(!rank[i]) continue;
            if(k) k --;
            int j = sa[rank[i] - 1];
            while(s[i + k] == s[j + k]) k ++;
            height[rank[i]] = k;
        }
    }
}
 
using SuffixArray::build;
using SuffixArray::height;
using SuffixArray::sa;
 
int main(){
 
    __fastIn;
 
    cin >> n >> m >> SuffixArray::s;
 
    build(128, n);
    LL ans = 0;
    for(int i = 0; i < n; i ++){
        ans += 1LL * max(0, n - sa[i] - max(height[i], m - 1));
    }
    cout << ans << endl;
 
    return 0;
}