kmp

KMP算法分两步 一：求子字符串（p）的next数组

void getnext(int nextt[],string p)
{
        nextt[0]=-1;
        for (int i=1;i<p.size();i++)
        {
            int j=nextt[i-1];
            while ((p[j+1]!=p[i])&&(j!=-1))
                j=nextt[j];
            if (p[j+1]==p[i])
                nextt[i]=j+1;
            else
                nextt[i]=-1;
        }
}

样例：

 

 

 

二：与主字符串（t）匹配

int kmp(int nextt[],string p,string t)
{
        getnext(nextt,p);
        int i=0,j=0;
        int ans=0;
        while (i<t.size())
        {
            if (p[j]==t[i])
            {
                i++;
                j++;
                if (j==p.size())
                {
                    ans++;
                    j=nextt[j-1]+1;
                }
            }
            else
            if (j==0)
                i++;
            else
                j=nextt[j-1]+1;
        }
        return ans; //ans就是要求的答案.
}

vjudge例题Oulipo完整代码如下

 

#include<bits/stdc++.h>
using namespace std;
int nextt[12345];
void getnext(int nextt[],string p)
{
        nextt[0]=-1;
        for (int i=1;i<p.size();i++)
        {
            int j=nextt[i-1];
            while ((p[j+1]!=p[i])&&(j!=-1))
                j=nextt[j];
            if (p[j+1]==p[i])
                nextt[i]=j+1;
            else
                nextt[i]=-1;
        }
}
int kmp(int nextt[],string p,string t)
{
        getnext(nextt,p);
        int i=0,j=0;
        int ans=0;
        while (i<t.size())
        {
            if (p[j]==t[i])
            {
                i++;
                j++;
                if (j==p.size())
                {
                    ans++;
                    j=nextt[j-1]+1;
                }
            }
            else
            if (j==0)
                i++;
            else
                j=nextt[j-1]+1;
        }
        return ans;
}
int main()
{
    std::ios::sync_with_stdio(false);//快输快出最好加上，不容易超时；
    std::cin.tie(0);
    std::cout.tie(0);
    string p,t;
    int n;
    cin>>n;
    while(n--)
    {
        cin>>p>>t;
        cout<<kmp(nextt,p,t)<<endl;
    }
    return 0;
}

 

 

 

 

标签：getnext,string,int,void,nextt,kmp
来源： https://www.cnblogs.com/xxj112/p/16201471.html