病毒侵袭持续中 HDU - 3065_purnu2-优快云博客

这篇博客主要介绍了AC自动机（Aho-Corasick算法）在字符串匹配中的应用，通过HDU-3065题目的AC代码，解释了如何避免WAWAWAWA错误，以及如何理解和构建字典树。博主详细讲解了代码流程，包括新节点创建、插入字符串、构建失败指针和查询过程，适合学习字符串算法的读者。

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题目链接

HDU-3065

AC代码

因为没有在文本串字符超出字典树范围之后重置now节点导致一直WAWAWAWA。
要理解板子呀！

#include <cstdio>
#include <cstring>
#include <queue>

using namespace std;

int const NUM = 5e4 + 10;
int const LEN = 26;
int const N = 2e6 + 6;

char str[1010][100];
char buf[N];
int nxt[NUM][LEN], fail[NUM], ed[NUM];
int root, L;
int cnt[NUM];

int newCode() {
    for (int i = 0; i < LEN; i++)
        nxt[L][i] = -1;
    ed[L] = 0;
    return L++;
}

void init() {
    memset(cnt, 0, sizeof(cnt));
    L = 0;
    root = newCode();
}

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

void insert(char *buf, int n) {
    int len = strlen(buf);
    int now = root;

    for (int i = 0; i < len; i++) {
        if (nxt[now][idx(buf[i])] == -1)
            nxt[now][idx(buf[i])] = newCode();
        now = nxt[now][idx(buf[i])];
    }

    ed[now] = n;
}

void build() {
    fail[root] = root;
    queue<int> q;

    for (int i = 0; i < LEN; i++) {
        if (nxt[root][i] == -1) nxt[root][i] = root;
        else {
            fail[nxt[root][i]] = root;
            q.push(nxt[root][i]);
        }
    }

    while (!q.empty()) {
        int now = q.front();
        q.pop();

        for (int i = 0; i < LEN; i++) {
            if (nxt[now][i] == -1) nxt[now][i] = nxt[fail[now]][i];
            else {
                fail[nxt[now][i]] = nxt[fail[now]][i];
                q.push(nxt[now][i]);
            }
        }
    }
}

void query(char *buf) {
    int len = strlen(buf);
    int now = root;

    for (int i = 0; i < len; i++) {
        if (buf[i] < 'A' || buf[i] > 'Z') {
            now = root;
            continue;
        }
        now = nxt[now][idx(buf[i])];
        int tmp = now;
        while (tmp != root) {
            if (ed[tmp] != 0)
                cnt[ed[tmp]] += 1;
            tmp = fail[tmp];
        }
    }
}

void print(int len) {
    for (int i = 1; i <= len; i++) {
        if (cnt[i] != 0)
            printf("%s: %d\n", str[i], cnt[i]);
    }
}

int main() {
    int n;
    while (scanf("%d", &n) != EOF) {
        init();
        for (int i = 1; i <= n; i++) {
            scanf("%s", str[i]);
            insert(str[i], i);
        }
        build();
        scanf("%s", buf);
        query(buf);
        print(n);
    }
    return 0;
}