POJ 3261 (后缀数组 二分) Milk Patterns

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int maxn = 20000 + 10;
const int maxm = 1000000 + 10;

int s[maxn];
int sa[maxn], height[maxn], rank[maxn];
int t[maxn], t2[maxn], c[maxm];
int n, k;

void build_sa(int m)
{
int i, *x = t, *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(int k = 1; k <= n; k <<= 1)
{
int p = 0;
for(i = n - k; i < n; i++) y[p++] = i;
for(i = 0; i < n; i++) if(sa[i] >= k) y[p++] = sa[i] - k;
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]]==y[sa[i-1]] && y[sa[i]+k]==y[sa[i-1]+k] ? p - 1 : p++;
if(p >= n) break;
m = p;
}
}

void build_height()
{
int i, j, k = 0;
for(i = 0; i < n; i++) rank[sa[i]] = i;
for(i = 0; i < n; i++)
{
if(k) k--;
j = sa[rank[i] - 1];
while(s[i + k] == s[j + k]) k++;
height[rank[i]] = k;
}
}

bool ok(int len)
{
int cnt = 0;
for(int i = 0; i < n; i++)
{
if(i == 0 || height[i] < len) cnt = 0;
if(++cnt >= k) return true;
}
return false;
}

int main()
{
//freopen("in.txt", "r", stdin);

scanf("%d%d", &n, &k);
for(int i = 0; i < n; i++)
{
scanf("%d", &s[i]);
s[i]++;
}
s
= 0;
build_sa(1000002);
build_height();

int L = 1, R = n;
while(L < R)
{
int M = (L + R + 1) / 2;
if(ok(M)) L = M;
else R = M - 1;
}

printf("%d\n", L);

return 0;
}