UVA 1399 - Puzzle

题目链接

题意：给定一些字符串，求一个最长的不在包含这些子串的字符串，如果可以无限长输出No

思路:建ACM自动机，把不可走结点标记构造出来，然后在这个状态图上进行dp找出最长路径即可，至于无限长的情况，只要在dp前进行一次dfs判有没有环即可

代码：

#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <map>
#include <queue>
using namespace std;

const int MAXNODE = 50005;
int n;

struct AutoMac {

    int ch[MAXNODE][26];
    int val[MAXNODE];
    int next[MAXNODE];
    int sz;

    void init() {
	sz = 1; 
	memset(ch[0], 0, sizeof(ch[0]));
    }

    int idx(char c) {
	return c - 'A';
    }

    void insert(char *str, int v = 1) {
	int n = strlen(str);
	int u = 0;
	for (int i = 0; i < n; i++) {
	    int c = idx(str[i]);
	    if (!ch[u][c]) {
		memset(ch[sz], 0, sizeof(ch[sz]));
		val[sz] = 0;
		ch[u][c] = sz++;
	    }
	    u = ch[u][c];
	}
	val[u] = v;
    }

    void getnext() {
	queue<int> Q;
	next[0] = 0;	
	for (int c = 0; c < n; c++) {
	    int u = ch[0][c];
	    if (u) {next[u] = 0; Q.push(u);}
	}

	while (!Q.empty()) {
	    int r = Q.front(); Q.pop();
	    for (int c = 0; c < n; c++) {
		int u = ch[r][c];
		if (!u) {
		    ch[r][c] = ch[next[r]][c];
		    continue;
		}
		Q.push(u);
		int v = next[r];
		while (v && !ch[v][c]) v = next[v];
		next[u] = ch[v][c];
		val[u] |= val[next[u]];
	    }
	}
    }
} gao;

int t, m, vis[MAXNODE], dp[MAXNODE], zh[MAXNODE][2], vv[MAXNODE];
char str[55];

bool find(int u) {
    vv[u] = 1;
    for (int i = 0; i < n; i++) {
	int v = gao.ch[u][i];
	if (vis[v]) return true;
	if (!vv[v] && !gao.val[v]) {
	    vis[v] = 1;
	    if (find(v)) return true;
	    vis[v] = 0;
	}
    }
    return false;
}

int dfs(int u) {
    if (vis[u]) return dp[u];
    vis[u] = 1;
    dp[u] = 0;
    for (int i = n - 1; i >= 0; i--) {
	if (!gao.val[gao.ch[u][i]]) {
	    int tmp = dfs(gao.ch[u][i]) + 1;
	    if (dp[u] < tmp) {
		dp[u] = tmp;
		zh[u][0] = gao.ch[u][i];
		zh[u][1] = i;
	    }
	}
    }
    return dp[u];
}

void print(int u) {
    if (zh[u][0] == -1) return;
    printf("%c", zh[u][1] + 'A');
    print(zh[u][0]);
}

int main() {
    scanf("%d", &t);
    while (t--) {
	gao.init();
	scanf("%d%d", &n, &m);
	while (m--) {
	    scanf("%s", str);
	    gao.insert(str);
	}
	gao.getnext();
	memset(vv, 0, sizeof(vv));
	memset(vis, 0, sizeof(vis));
	vis[0] = 1;
	if (find(0)) printf("No\n");
	else {
	    memset(vis, 0, sizeof(vis));
	    memset(zh, -1, sizeof(zh));
	    if (dfs(0) == 0) printf("No\n");
	    else {
		print(0);
		printf("\n");
	    }
	}
    }
    return 0;
}