字符串

hash

poj3461 Oulipo

#include<cstdio>
#include<cstring>
#define ull unsigned long long
using namespace std; 
ull power[1000005],sum[1000005];
char s1[10005],s2[1000005];
int main()
{
    int t,b = 26;
    scanf("%d",&t);
    power[0] = 1;
    for(int i = 1;i <= 1000000;i++)
        power[i] = power[i - 1] * b;
    while(t--)
    {
        scanf("%s%s",s1 + 1,s2 + 1);
        int n = strlen(s1 + 1),m = strlen(s2 + 1);
        sum[0] = 0;
        for(int i = 1;i <= m;i++)
            sum[i] = sum[i - 1] * b + (ull)(s2[i] - 'A' + 1);
        ull s = 0;
        for(int i = 1;i <= n;i++)
            s = s * b +(ull)(s1[i] - 'A' + 1);
        int ans = 0;
        for(int i = 0;i <= m - n;i++)
            if(s == sum[i + n] - sum[i] * power[n])
                ans++;
        printf("%d\n",ans);
    }
    return 0;
}

 

kmp

hdu2087 剪花布条

#include<cstdio>
#include<cstring>
using namespace std;
const int N = 1010;

char a[N],b[N];
int n,m;
int nxt[N];
void prepare()
{
    nxt[1] = 0;
    int j = 0;
    for(int i = 1;i < m;i++)
    {
        while(j > 0 &&b[j + 1] != b[i + 1])
            j = nxt[j];
        if(b[j + 1] == b[i + 1])
            j++;
        nxt[i + 1] = j;
    }
}
int kmp()
{
    int ans = 0,j = 0;
    for(int i = 0;i < n;i++)
    {
        while(j > 0 && b[j + 1] != a[i + 1])
            j = nxt[j];
        if(b[j + 1] == a[i + 1])
            j++;
        if(j == m)
        {
            j = 0;
            ans++;
        }
    }
    return ans;
}
int main()
{
    while(~scanf("%s",a+1))
    {
        n = strlen(a + 1);
        if(a[1] == '#' && n == 1)
            break;
        scanf("%s",b+1);        
        m = strlen(b + 1);
        prepare();
        printf("%d\n",kmp());        
    }
    return 0;
} 

 

trie字典树

poj3630 Phone List

#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int N = 1e5 + 10;
int n,tot;
bool bo[N];
int num[N][15];//num[u][c]以u为父节点，边权为c 
char s[15];
void clear()
{
    memset(num,0,sizeof(num));
    memset(bo,0,sizeof(bo));
}
bool insert(char *s)
{
    int len = strlen(s);
    int u = 1;
    bool flag = false;
    for(int i = 0;i < len;i++)
    {
        int c = s[i] - '0';
        if(!num[u][c])
            num[u][c] = ++tot;
        else if(i == len - 1)//新加入的字符串和以前的相同或者包毫爽以前的 
            flag = true;
        u = num[u][c];
        if(bo[u])
            flag = true;    
    }
    bo[u] = true;
    return flag;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        tot = 1;
        clear();
        bool ans = false;
        for(int i = 1;i <= n;i++)
        {
            scanf("%s",s);
            if(insert(s))
                ans = true;
        }
        if(!ans)
            puts("YES");
        else
            puts("NO");
    }
    return 0;
}

 

AC自动机

洛谷3808 模板

#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
const int N = 1e6 + 10;
int n;
char s[N];
queue<int> q;
struct AC
{
    int ch[N>>1][26],val[N>>1],nxt[N>>1],tot;
    void  insert(char *s)
    {
        int len = strlen(s);
        int now = 0;
        for(int i = 0;i < len;i++)
        {
            int v = s[i] - 'a';
            if(!ch[now][v])
                ch[now][v] = ++tot;
            now = ch[now][v];
        }
        val[now]++;
    }
    void build()
    {
        for(int i = 0;i <= 25;i++)
            if(ch[0][i])
            {
                nxt[ch[0][i]] = 0;
                q.push(ch[0][i]);
            }
        while(!q.empty())
        {
            int u = q.front();
            q.pop();
            for(int i = 0;i < 26;i++)
                if(ch[u][i])
                {
                    nxt[ch[u][i]] = ch[nxt[u]][i];
                    q.push(ch[u][i]);
                }
                else
                    ch[u][i] = ch[nxt[u]][i]; 
        }
    }
    int query(char *s)
    {
        int len = strlen(s);
        int now = 0,ans = 0;
        for(int i = 0;i < len;i++)
        {
            now = ch[now][s[i] - 'a'];
            for(int t = now;t && ~val[t];t = nxt[t])
            {
                ans += val[t];
                val[t] = -1;
            }
        }
        return ans;
    }
}ac;
int main()
{
    scanf("%d",&n);
    for(int i = 1;i <= n;i++)
    {
        scanf("%s",s);
        ac.insert(s);
    }
    ac.build();
    scanf("%s",s);
    int ans = ac.query(s);
    printf("%d",ans);
    return 0;
}