POJ 2774

求两串的最长相同公共连续子串

将两串拼接在一起，中间用一个未出现过的符号隔开

求 sa, height

sa[i] 与 sa[i-1] 不在同一个串时的 height[i] 的最大值就是答案

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
const int MAXN = 200005;

struct SuffixArray
{
    int wa[MAXN], wb[MAXN], wsf[MAXN], wv[MAXN];
    int Cmp(int r[], int a, int b, int k)
    {
        return r[a] == r[b] && r[a+k] == r[b+k];
    }
    void GetSa(int r[], int sa[], int n, int m)
    {
        int i, j, p, *x = wa, *y = wb, *t;
        for (i = 0; i < m; i++) wsf[i] = 0;
        for (i = 0; i < n; i++) wsf[x[i]=r[i]]++;
        for (i = 1; i < m; i++) wsf[i] += wsf[i-1];
        for (i = n - 1; i >= 0; i--) sa[--wsf[x[i]]] = i;
        for (p = j = 1; p < n; j *= 2, 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 < n; i++) wv[i] = x[y[i]];
            for (i = 0; i < m; i++) wsf[i] = 0;
            for (i = 0; i < n; i++) wsf[wv[i]]++;
            for (i = 1; i < m; i++) wsf[i] += wsf[i-1];
            for (i = n-1; i >= 0; i--) sa[--wsf[wv[i]]] = y[i];
            swap(x, y);
            x[sa[0]] = 0;
            for (p = i = 1; i < n; i++)
                x[sa[i]] = Cmp(y, sa[i-1], sa[i], j) ? p - 1: p++;
        }
    }
    void GetHeight(int r[], int sa[], int rnk[], int height[], int n)
    {
        int i, j, k = 0;
        for (i = 1; i <= n; i++)
            rnk[sa[i]] = i;
        for (i = 0; i < n; i++)
        {
            if (k) k--;
            j = sa[rnk[i]-1];
            while (r[i+k] == r[j+k]) k++;
            height[rnk[i]] = k;
        }
    }
    
}suffixArray;
int r[MAXN], sa[MAXN], rnk[MAXN], height[MAXN];
char s[MAXN];
int len1, len2;
bool check(int i, int j)
{
    return ( sa[i] < len1 && sa[j] > len1 ) ||
           ( sa[i] > len1 && sa[j] < len1 ) ;
}
int main()
{
    scanf("%s",s);
    len1 = strlen(s);
    s[len1] = '#';
    scanf("%s", s + len1 + 1);
    len2 = strlen(s);
    int m = 0;
    for (int i = 0; i < len2; i++)
    {
        if(i == len1) r[i] = 1;
        else r[i] = s[i] - 'a' + 2;
        m = max(r[i] + 1, m);
    }
    r[len2] = 0;
    suffixArray.GetSa(r, sa, len2 + 1, m);
    suffixArray.GetHeight(r, sa, rnk, height, len2);
    int ans = 0;
    for (int i = 1; i < len2; i++)
    {
        if(check(i,i-1))
        {
            ans = max(height[i], ans);
        }
    }
    printf("%d
", ans);
}