poj 3261 Milk Patterns 后缀数组

题目链接

求可重叠k次的最长子串。

二分子串长度x， 将height数组分组， 看是否有一组中的数量大于等于k。

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <queue>
#include <stack>
#include <bitset>
using namespace std;
#define pb(x) push_back(x)
#define ll long long
#define mk(x, y) make_pair(x, y)
#define lson l, m, rt<<1
#define mem(a) memset(a, 0, sizeof(a))
#define rson m+1, r, rt<<1|1
#define mem1(a) memset(a, -1, sizeof(a))
#define mem2(a) memset(a, 0x3f, sizeof(a))
#define rep(i, n, a) for(int i = a; i<n; i++)
#define fi first
#define se second
typedef pair<int, int> pll;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int mod = 1e9+7;
const int inf = 1061109567;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
const int maxn = 2e4+5;
int sa[maxn];
int t1[maxn],t2[maxn],c[maxn], a[maxn];
int rankk[maxn],height[maxn];
void build_sa(int s[],int n,int m)
{
    int i,j,p,*x=t1,*y=t2;
    for(i=0;i<m;i++)c[i]=0;
    for(i=0;i<n;i++)c[x[i]=s[i]]++;
    for(i=1;i<m;i++)c[i]+=c[i-1];
    for(i=n-1;i>=0;i--)sa[--c[x[i]]]=i;
    for(j=1;j<=n;j<<=1)
    {
        p=0;
        for(i=n-j;i<n;i++)y[p++]=i;
        for(i=0;i<n;i++)if(sa[i]>=j)y[p++]=sa[i]-j;
        for(i=0;i<m;i++)c[i]=0;
        for(i=0;i<n;i++)c[x[y[i]]]++;
        for(i=1;i<m;i++)c[i]+=c[i-1];
        for(i=n-1;i>=0;i--)sa[--c[x[y[i]]]]=y[i];
        swap(x,y);
        p=1;x[sa[0]]=0;
        for(i=1;i<n;i++)
            x[sa[i]]=y[sa[i-1]]==y[sa[i]] && y[sa[i-1]+j]==y[sa[i]+j]?p-1:p++;
        if(p>=n)break;
        m=p;
    }
}
void getHeight(int s[],int n)
{
    int i,j,k=0;
    for(i=0;i<=n;i++)rankk[sa[i]]=i;
    for(i=0;i<n;i++)
    {
        if(k)k--;
        j=sa[rankk[i]-1];
        while(s[i+k]==s[j+k])k++;
        height[rankk[i]]=k;
    }
}
int check(int mid, int n, int m) {
    int cnt = 1;
    for(int i = 1; i<=n; i++) {
        if(height[i]>=mid) {
            cnt++;
            if(cnt>=m)
                return 1;
        } else {
            cnt = 1;
        }
    }
    return 0;
}
int main()
{
    int n, m;
    while(cin>>n>>m) {
        int maxx = 0;
        for(int i = 0; i<n; i++) {
            scanf("%d", &a[i]);
            maxx = max(maxx, a[i]);
        }
        a[n] = 0;
        build_sa(a, n+1, maxx+1);
        getHeight(a, n);
        int l = 1, r = n, ans;
        while(l<=r) {
            int mid = l+r>>1;
            if(!check(mid, n, m)) {
                r = mid-1;
            } else {
                l = mid+1;
                ans = mid;
            }
        }
        cout<<ans<<endl;
    }
    return 0;
}