KMP算法

KMP算法

 字符串的快速匹配

package cn.wubowei;

public class KMP {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
         String pattern="ABABCABAA";
         char[] patternch=pattern.toCharArray();
         char[] text="ABABABABCABAAABAB".toCharArray();
         int n= pattern.length();
         int[] prefix=new int[n];
//         prefixtable(patternch, prefix, n);
//         movePrefixTable(prefix, n);
         kmpsearch(text, patternch);
         
    }
    public  static void prefixtable (char pattern[], int prefix[], int n) {
        prefix[0]=0;
        int len=0;
        int i=1;
        while (i<n) {
            if(pattern[i] == pattern[len]) {
                len++;
                prefix[i]=len;
                i++;
            }else {
                if(len>0) {
                len =prefix[len-1];
                }else {
                    prefix[i]= len;
                    i++;
                }
            }
        }
    }
    
    public static void movePrefixTable(int prefix[], int n) {
//        int i=0;
        for(int i=n-1;i>0;i--) {
            prefix[i]=prefix[i-1];
        }
        prefix[0]=-1;
    }
    
    public static void kmpsearch (char text[], char pattern[]) {
        int n= pattern.length;
        int m=text.length;
        int[] prefix=new int[n];
        prefixtable(pattern, prefix, n);
        movePrefixTable(prefix,n);
        int i=0;
        int j=0;
    
        while(i<m) {
            if(j==n-1&&text[i]==pattern[j]) {
                System.out.println(i-j);
                j=prefix[j];
            }
            if(text[i]== pattern[j]) {
                i++;
                j++;
            }else {
                j=prefix[j];
                if(j==-1) {
                    i++;j++;
                }
                    
            }
        }
    }
    
}