题意：训练指南P225
分析：二分寻找长度，用hash值来比较长度为L的字串是否相等。
#include <bits/stdc++.h>
using namespace std; typedef unsigned long long ull;
const int N = 4e4 + 5;
const int x = 123;
ull H[N], _hash[N], xp[N];
int rk[N];
char str[N];
int m; void get_hash(char *s, int len) {
H[len] = 0;
for (int i=len-1; i>=0; --i) {
H[i] = H[i+1] * x + (s[i] - 'a');
}
xp[0] = 1;
for (int i=1; i<len; ++i) {
xp[i] = xp[i-1] * x;
}
} bool cmp(const int &a, const int &b) {
return (_hash[a] < _hash[b] || (_hash[a] == _hash[b] && a < b));
} int check(int L, int len) {
int cnt = 0, pos = -1, c = 0;
for (int i=0; i<len-L+1; ++i) {
rk[i] = i;
_hash[i] = H[i] - H[i+L] * xp[L];
}
sort (rk, rk+len-L+1, cmp);
for (int i=0; i<len-L+1; ++i) {
if (i == 0 || _hash[rk[i]] != _hash[rk[i-1]]) c = 0;
if (++c >= m) pos = max (pos, rk[i]);
}
return pos;
} int main(void) {
while (scanf ("%d", &m) == 1) {
if (!m) break;
scanf ("%s", &str);
int len = strlen (str);
get_hash (str, len);
if (check (1, len) == -1) puts ("none");
else {
int l = 1, r = len + 1;
while (r - l > 1) {
int mid = l + r >> 1;
if (check (mid, len) >= 0) l = mid;
else r = mid;
}
printf ("%d %d\n", l, check (l, len));
}
} return 0;
}
后缀数组也可以求解，具体就是二分答案，height数组分组判断是否满足存在题意的解，并使最优。（m=1时特判处理）
#include <bits/stdc++.h> const int N = 4e4 + 5;
int sa[N], rank[N], height[N];
int ws[N], wa[N], wb[N];
char s[N]; bool cmp(int *r, int a, int b, int l) {
return (r[a] == r[b] && r[a+l] == r[b+l]);
}
void DA(char *r, int n, int m = 128) {
int i, j, p, *x = wa, *y = wb;
for (i=0; i<m; ++i) ws[i] = 0;
for (i=0; i<n; ++i) ws[x[i]=r[i]]++;
for (i=1; i<m; ++i) ws[i] += ws[i-1];
for (i=n-1; i>=0; --i) sa[--ws[x[i]]] = i;
for (j=1, p=1; p<n; j<<=1, m=p) {
for (p=0, 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) ws[i] = 0;
for (i=0; i<n; ++i) ws[x[y[i]]]++;
for (i=1; i<m; ++i) ws[i] += ws[i-1];
for (i=n-1; i>=0; --i) sa[--ws[x[y[i]]]] = y[i];
std::swap (x, y);
for (p=1, x[sa[0]]=0, i=1; i<n; ++i) {
x[sa[i]] = cmp (y, sa[i-1], sa[i], j) ? p - 1 : p++;
}
}
}
void calc_height(char *r, int *sa, int n) {
int i, j, k = 0;
for (i=1; i<=n; ++i) rank[sa[i]] = i;
for (i=0; i<n; ++i) {
if (k) k--;
j = sa[rank[i]-1];
while (r[i+k] == r[j+k]) k++;
height[rank[i]] = k;
}
} int m;
int check(int len, int n) {
int p = -1;
int cnt = 0, ret = -1;
for (int i=1; i<=n; ++i) {
if (height[i] >= len) {
if (p == -1) {
p = std::max (sa[i-1], sa[i]);
} else {
p = std::max (p, std::max (sa[i-1], sa[i]));
}
cnt++;
if (cnt + 1 >= m) {
ret = std::max (ret, p);
}
} else {
p = -1;
cnt = 0;
}
}
return ret;
} int main() {
while (scanf ("%d", &m) == 1) {
if (!m) break;
scanf ("%s", s);
int n = strlen (s); if (m == 1) {
printf ("%d %d\n", n, 0);
continue;
} DA (s, n + 1);
calc_height (s, sa, n); int best = 0, pos = -1;
int left = 0, right = n;
while (left <= right) {
int mid = left + right >> 1;
int res = check (mid, n);
if (res != -1) {
if (best < mid) {
best = mid;
pos = res;
} else if (mid > 0 && best == mid && pos < res) {
pos = res;
}
left = mid + 1;
} else {
right = mid - 1;
}
}
if (pos == -1) {
puts ("none");
} else {
printf ("%d %d\n", best, pos);
}
} return 0;
}