2020牛客暑期多校训练营（第四场) B Count New String

题解：建议看官方题解

#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
typedef long long LL;
typedef pair<int, int> pii;
const int maxn = 3e6 + 50;
struct state
{
    int len, link;    
    int nex[26];
} st[maxn * 2];

int sz, last;
void sam_init(){
    st[0].len = 0;
    st[0].link = -1;
    sz = 1, last = 0;
}
int stk[maxn], top, pos[maxn];
int sam_extend(int c){
    int cur = sz++;
    st[cur].len = st[last].len + 1;
    int p = last;
    last = cur;
    while(p != -1 && !st[p].nex[c]){
        st[p].nex[c] = cur;
        p = st[p].link;
    }
    if(p == -1){
        st[cur].link = 0;
        return last;
    } 
    int q = st[p].nex[c];
    if(st[q].len == st[p].len + 1){
        st[cur].link = q;
        return last;
    }
    int clone = sz++;
    st[clone].len = st[p].len + 1;
    for(int i = 0; i < 26; i++){
        st[clone].nex[i] = st[q].nex[i];
    }
    st[clone].link = st[q].link;
    while(p != -1 && st[p].nex[c] == q){
        st[p].nex[c] = clone;
        p = st[p].link;
    }
    st[q].link = st[cur].link = clone;
    return last;
}

string s;
int main() {
    std::ios::sync_with_stdio(false);
    cin >> s;
    int n = s.size();
    pos[n] = 0;
    stk[1] = n;
    s[n] = 'z' + 1;
    top = 1;
    sam_init();
    for(int i = n - 1; i >= 0; i--){
        while(s[i] - 'a' > s[stk[top]] - 'a' && top) {
            top--;
        }
        last = pos[stk[top]];
        for(int j = i; j < stk[top]; j++) {
            last = sam_extend(s[i] - 'a');
        }
        pos[i] = last;
        stk[++top] = i;
    }
    LL ans = 0;
    for(int i = 1; i < sz; i++) ans += st[i].len - st[st[i].link].len;
    cout << ans << '\n';
}