java实现字符串kmp算法

最新推荐文章于 2025-01-11 17:14:05 发布

转载最新推荐文章于 2025-01-11 17:14:05 发布 · 572 阅读

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本文详细介绍了KMP算法的实现过程，包括next数组的计算、字符串匹配的基本原理及应用实例。

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package test;

public class StringKMP {

   public void getNextBetter(String str, int[] next){
       int len = str.length();
       next[1] = 0;
       int i = 1;
       int j = 0;
       while(i < len - 1){
           if(j == 0 || str.charAt(i) == str.charAt(j)){
               ++ i;
               ++ j;
               if(str.charAt(i) != str.charAt(j)){
                   next[i] = j;
               } else{
                   next[i] = next[j];
               }

           } else {
               j = next[j];
           }
       }
   }
   public void getNext(String str, int[] next){
       int len = str.length();
       next[1] = 0;
       int i = 1;
       int j = 0;
       while(i < len - 1){
           if(j == 0 || str.charAt(i) == str.charAt(j)){
               ++ i;
               ++ j;
               next[i] = j;
           } else {
               j = next[j];
           }
       }
   }
   public int getIndex(String strLong, String strShort, int pos){

       int lenLong = strLong.length();
       int lenShort = strShort.length();

       strLong = "x" + strLong;
       strShort = "x" + strShort;

       int[] next = new int[lenShort + 1];
       this.getNextBetter(strShort, next);

       int i = pos + 1;
       int j = 1;

       while(i <= lenLong && j <= lenShort){
           if(j == 0 || strLong.charAt(i) == strShort.charAt(j)){
               ++ i;
               ++ j;
           } else{
               j = next[j];
           }
       }
       if(j > lenShort)
           return i-lenShort-1;
       else
           return 0;
   }
   public static void main(String[] args) {
       // TODO Auto-generated method stub
       String strLong = "ertsafabaabcacseadfsdg";
       String strShort = "abaabcac";

       StringKMP kmp = new StringKMP();

       int index = kmp.getIndex(strLong,strShort,0);
       System.out.println(index);
   }

}