spoj 1811 LCS - Longest Common Substring (后缀自动机)

标签：algorithm   字符串   后缀自动机   

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
const int N = 3 * 1e5;
char S[N], T[N];

struct SAM {
	struct Node {
		int fa, ch[27];
		int val;
		void init() {
			fa = val = 0;
			memset(ch, 0, sizeof(ch));
		}
	} node[2 * N];
	
	int tot;
	int new_node() {
		node[++tot].init();
		return tot;
	}

	int root, last;
	void init() {
		tot = root = last = 1;
		node[0].init();
		node[1].init();
	}

	void add(int x) {
		int p = last;
		int np = new_node(); node[np].val = node[p].val + 1;
		while(p && node[p].ch[x] == 0){
			node[p].ch[x] = np;
			p = node[p].fa;
		}
		if(p == 0) node[np].fa = root;
		else {
			int q = node[p].ch[x];
			if(node[p].val + 1 == node[q].val)
				node[np].fa = q;
			else {
				int nq = new_node(); node[nq].val = node[p].val + 1;
				memcpy(node[nq].ch, node[q].ch, sizeof(node[q].ch));
				node[nq].fa = node[q].fa;
				node[q].fa = node[np].fa = nq;
				while(p && node[p].ch[x] == q) {
					node[p].ch[x] = nq;
					p = node[p].fa;
				}
			}
		}
		last = np;
	}
	void debug() {
		for(int i = 1; i <= tot; ++i) {
			printf("id=%d, fa=%d, step=%d, ch=[ ", i, node[i].fa, node[i].val);
			for(int j = 0; j < 26; ++j) {
				if(node[i].ch[j])
					printf("%c,%d ", j+'a', node[i].ch[j]);
			}
			puts("]");
		}
	}

	void gao();
} sam;

void SAM::gao() {
	int len_s = strlen(S);
	int len_t = strlen(T);
	
	init();
	for(int i = 0; i < len_s; ++i) {
		add(S[i] - 'a');
	}
	//debug();
	int p = root;
	int ans = 0;
	int tmp = 0;
	for(int i = 0; i < len_t; ++i) {
		if(node[p].ch[T[i] - 'a']) {
			++tmp;
			p = node[p].ch[T[i] - 'a'];
		} else {
			while(p && node[p].ch[T[i] - 'a'] == 0)
				p = node[p].fa;
			if(p) {
				tmp = node[p].val + 1;
				p = node[p].ch[T[i] - 'a'];
			} else {
				p = root;
				tmp = 0;
			}
		}
		ans = max(ans, tmp);
	}
	printf("%d\n", ans);
}

int main() {
	scanf("%s%s", S, T);
	sam.gao();
	return 0;
}

spoj 1811 LCS - Longest Common Substring (后缀自动机)

标签：algorithm   字符串   后缀自动机   

原文地址：http://blog.csdn.net/whai362/article/details/47667285