KMP算法（java,c++）

Posted 2021-12-01 cky-2907183182

//java

public class KMP {
    public static int[] getNextArray(char[] t) {
        int[] next = new int[t.length];
        next[0] = -1;
        next[1] = 0;
        int k;
        for (int j = 2; j < t.length; j++) {
            k=next[j-1];
            while (k!=-1) {
                if (t[j - 1] == t[k]) {
                    next[j] = k + 1;
                    break;
                }
                else {
                    k = next[k];
                }
                next[j] = 0;  //当k==-1而跳出循环时，next[j] = 0，否则next[j]会在break之前被赋值
            }
        }
        return next;
    }
    public static int kmpMatch(String s, String t){
        char[] s_arr = s.toCharArray();
        char[] t_arr = t.toCharArray();
        int[] next = getNextArray(t_arr);
        int i = 0, j = 0;
        while (i<s_arr.length && j<t_arr.length){
            if(j == -1 || s_arr[i]==t_arr[j]){
                i++;
                j++;
            }
            else
                j = next[j];
        }
        if(j == t_arr.length)
            return i-j;
        else
            return -1;
    }

    public static void main(String[] args) {
        System.out.println(kmpMatch("abcabaabaabcacb", "abaabcac"));
    }

}

 

 

//c++

#include <iostream>
#include <string>

using namespace std;
int next[8];
/*求单个回溯值
int GetNext(int j,char T[])
{
    if(j==0) return -1;
    if(j>0)
    {
        int k=GetNext(j-1,T);
        while (k>=0)
            if(T[j-1]==T[k]) return k+1;
            else k=GetNext(k,T);
        return 0;
    }
    return 0;
}*/
void GetNext(char T[])
{
    int j=0,k=-1;next[j]=k;
    while (T[j]!=‘\0‘)
        if(k==-1 || T[j]==T[k])
        {j=j+1;k=k+1;next[j]=k;}
        else k=next[k];
}
int KMP(char S[],int start,char T[])
{   int i=start,j=0;
    while (S[i]!=‘\0‘&&T[j]!=‘\0‘)
    if(j==-1||S[i]==T[j])
        {i=i+1;j=j+1;}
    else j=next[j];
    if(T[j]==‘\0‘) return(i-j);
    else return(-1);

}



int main()
{   //字符数组检测不到"\0"
    //char S[]={‘d‘,‘f‘,‘g‘,‘a‘,‘b‘,‘a‘,‘a‘,‘b‘,‘c‘,‘a‘,‘c‘,‘f‘};
    //char T[]={‘a‘,‘b‘,‘a‘,‘a‘,‘b‘,‘c‘,‘a‘,‘c‘};
    char S[]="gfylaa45e4daabaabcac";
    char T[]="abaabcac";
    GetNext(T);
    for(int i=0;i<8;i++)
        cout<<next[i]<<‘ ‘;
    cout<<endl;
    cout<<KMP(S,0,T)<<endl;


    return 0;

}