【SuffixArray】bzoj1717 [Usaco2006 Dec] Milk Patterns 產奶的模式

傳送門：BZOJ1717

解題思路

先把正解說一說：單調隊列或者二分
然後麼。。爲什麼我寫的這麼長？！
是羅穗騫的論文題嘛……就當給後綴數組練手吧
可重疊k次重複字串

YM代碼

#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for(int i = (a); i <= (b); i++)
#define red(i, a, b) for(int i = (a); i >= (b); i--)
#define ll long long

inline int read() {
    int x = 0;
    char ch = getchar();
    while(ch < '0' || ch > '9') ch = getchar();
    while(ch >= '0' || ch <= '9') {
        x *= 10; x += ch - '0';
        ch = getchar();
    }
    return x;
}

const int N = 20005;
int n, m, k, p, q, tot = 0;
int a[N], num[N], hash[N], v[N], h[N], height[N], sa[2][N], rank[2][N];

int find(int x) {
    int l = 1, r = tot, ans = 0;
    while(l <= r) {
        int mid = (l + r) >> 1;
        if (hash[mid] <= x) ans = mid, l = mid + 1;
        else r = mid - 1;
    }
    return ans;
}

bool jud(int x) {
    int tmp = 0;
    rep(i, 1, n) {
        if (height[i] >= x) {
            tmp++;
            if (tmp == m-1) return 1;
        }else tmp = 0;
    }
    return 0;
}

void getans() {
    k = 0;
    rep(i, 1, n) {
        if (rank[p][i] == 1) h[i] = 0;
        else {
            int j = sa[p][rank[p][i]-1];
            while(a[i+k] == a[j+k]) k++;
            h[i] = k;
            if (k > 0) k--;
        }
    }
    rep(i, 1, n) height[rank[p][i]] = h[i];
    int l = 1, r = n, ans = 0;
    while(l <= r) {
        int mid = (l + r) >> 1;
        if (jud(mid)) ans = mid, l = mid + 1;
        else r = mid - 1;
    }
    printf("%d\n", ans);
}

void calsa(int sa[N], int rk[N], int SA[N], int RK[N]) {
    rep(i, 1, n) v[rk[sa[i]]] = i;
    red(i, n, 1) if (sa[i] > k) SA[v[rk[sa[i]-k]]--] = sa[i] - k;
    rep(i, n-k+1, n) SA[v[rk[i]]--] = i;
    rep(i, 1, n) RK[SA[i]] = RK[SA[i-1]] + (rk[SA[i]] != rk[SA[i-1]] || rk[SA[i]+k] != rk[SA[i-1]+k]);
}

void work() {
    p = 0, q = 1; a[0] = -1;
    rep(i, 1, n) v[a[i]]++;
    rep(i, 1, n) v[i] += v[i-1];
    rep(i, 1, n) sa[p][v[a[i]]--] = i;
    rep(i, 1, n)
        if(a[sa[p][i]] != a[sa[p][i-1]])
             rank[p][sa[p][i]] = rank[p][sa[p][i-1]] + 1;
        else rank[p][sa[p][i]] = rank[p][sa[p][i-1]];
    k = 1;
    while(k < n) {
        calsa(sa[p], rank[p], sa[q], rank[q]);
        p^=1; q^=1; k<<=1;
    }
    getans();
}

int main() {
    scanf("%d%d", &n, &m);
    rep(i, 1, n) {
        scanf("%d", &a[i]);
        num[i] = a[i];
    }
    sort(num + 1, num + n + 1);
    hash[++tot] = num[1];
    rep(i, 2, n) {
        if (num[i] != num[i-1]) 
            hash[++tot] = num[i];
    }
    rep(i, 1, n) a[i] = find(a[i]);
    work();
    return 0;
}

尾聲

好長好長…好長好長…
真的不想…一直做碼題～～

End.