KMP算法 java版本

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1 原理

参考《大话数据结构》第5章串的第5.7小节 : KMP模式匹配算法

2 java代码

KMP.java

package leaning.string.KMP;public class KMP {public static int indexKMP(String source, String target,int pos) {/* i 用于主串source当前位置下标值，若pos不为1 则从pos位置开始匹配 */int i = pos ; /* j 用于子串 target中当前位置下标值 */int j = 1 ;/*定义一组next数组*/int[] next = new int[IntArrayLength.length];  /*对target进行分析,得到next数组*/next = NextUtil.getNext(target);// 将source,target字符串变为字符数组char[] sourceChar = KMPStringUtil.stringToChar(source);char[] targetChar = KMPStringUtil.stringToChar(target);//若i小于source长度并且target小于target长度,执行循环while(i <=source.length() && j <= target.length() ){if(j==0 || sourceChar[i] == targetChar[j] ){++i;++j;}else{j = next[j] ;}}if( j > target.length() ){return i - target.length();}else{return 0;}}public static void main(String args[]) {String source = "asdkfjslkfjwejdklfjew8odklfjsdlkfjslkdj";String target = "w8odkl";int pos = 0;int p  = KMP.indexKMP(source, target, pos);System.out.println("在位置 " +p + "完全匹配");}}

NextUtil.java

package leaning.string.KMP;public class NextUtil {/** *  * 得到next数组  * */public static int[] getNext( String targetStr) {       if(targetStr==null) return null;       char[] targetModify = KMPStringUtil.stringToChar(targetStr); // 将targetStr字符串改为字符数组       int length = targetStr.length();       // 得到next数组       int i,j;       i = 1 ;       j = 0 ;       int next[] = new int[IntArrayLength.length];       while( i < length){       if(j == 0 || targetModify[i] == targetModify[j]){ // targetModify[i]表示后缀单个字符, targetModify[j]表示前缀的单个字符        ++i;       ++j;       next[i] = j ;       }else{       j = next[j]; // 若字符不同，则 j 进行回溯       }       }          return next;}  public static void main(String args[]){String targetStr = "ababaaaba" ;int next[] = NextUtil.getNext(targetStr);for(int i = 0 ; i < next.length ; i++){System.out.print(next[i] + " ");}}}

IntArrayLength.java

package leaning.string.KMP;public  class IntArrayLength {   public  static int length = 255;}

KMPStringUtil.java

package leaning.string.KMP;public class KMPStringUtil {   public static char[] stringToChar(String source){        /**        * 对source进行改造,使其第一位为一个占位符        *    source =    a b c d e f g h        * targetModify = '' a b c d e f g h         *         * */       char[] targetModify = new char[source.length()+1];       int length = source.length() ;        for(int i = 0 ; i < source.length() ; i++){       targetModify[i+1] = source.charAt(i);       }return targetModify;} }

3 运行结果

运行 KMP.java 得到下面结果

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