POJ 2774 (后缀数组 最长公共字串) Long Long Message

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

const int maxn = 200000 + 10;

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

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

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

scanf("%s", s);
int pos = strlen(s);
s[pos] = 1;
scanf("%s", s + pos + 1);
n = strlen(s);

build_sa(n + 1, 256);
build_height();

int ans = 0;
for(int i = 2; i <= n; i++)
{
if(height[i] > ans)
{
if((sa[i]>pos && sa[i-1]<pos) || (sa[i]<pos&&sa[i-1]>pos))
ans = height[i];
}
}

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

return 0;
}