用后缀数组求两个串的最长公共子串的长度
详见罗穗骞的论文
#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <cstdlib>
#define MAXN 1000005
using namespace std;
int r[MAXN];
int wa[MAXN], wb[MAXN], wv[MAXN], tmp[MAXN];
int sa[MAXN]; //index range 1~n value range 0~n-1
int cmp(int *r, int a, int b, int l)
{return r[a] == r[b] && r[a + l] == r[b + l];
}
void da(int *r, int *sa, int n, int m)
{int i, j, p, *x = wa, *y = wb, *ws = tmp;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 *= 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++) ws[i] = 0;for (i = 0; i < n; i++) ws[wv[i]]++;for (i = 1; i < m; i++) ws[i] += ws[i - 1];for (i = n - 1; i >= 0; i--) sa[--ws[wv[i]]] = y[i];for (swap(x, y), 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++;}
}
int rank[MAXN]; //index range 0~n-1 value range 1~n
int height[MAXN]; //index from 1 (height[1] = 0)
void calheight(int *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; height[rank[i++]] = k)for (k ? k-- : 0, j = sa[rank[i] - 1]; r[i + k] == r[j + k]; ++k);return;
}
char s1[MAXN], s2[MAXN];
int main()
{while(scanf("%s%s", s1, s2) != EOF){int len = strlen(s1);strcat(s1, "$");strcat(s1, s2);int n = strlen(s1), m = 0;for(int i = 0; i < n; i++){m = max(m, (int)s1[i]);r[i] = s1[i];} r[n] = 0;da(r, sa, n + 1, m + 1); //注意是n + 1 ，原因去看论文calheight(r, sa, n);int res = 0;for(int i = 1; i < n; i++)if((sa[i - 1] < len && sa[i] >= len) || (sa[i - 1] >= len && sa[i] < len)) res = max(res, height[i]);printf("%d\n", res);}return 0;
}