KMP

package jiegouSuanfa;
/**
 * KMP算法字符串匹配
 * @author 97699
 *
 */
public class KMP {
	/**
	 * 暴力方法
	 * @param lstr
	 * @param str
	 * @return
	 */
	 public static int  bl(String lstr,String str) {
		char[] a=lstr.toCharArray();
		char[] b=str.toCharArray();
		int i=0;
		int j=0;
		while(i<a.length&&j<b.length) {
			if(a[i]==b[j]) {
				i++;
				j++;
			}else {
				i=i-j+1;
				j=0;
			}
		}
		if(j==b.length) {
			return i-j;
		}else {
			return -1;
		}
	}

	public static void main(String[] args) {
		String lstr="abcabdadf";
		String str="bdad";
		int m=bl(lstr,str);
		int n=KMP(lstr,str);
		System.out.println("暴力方法求解："+m);
		System.out.println("KMP:"+n);
	}

	public static int KMP(String lstr, String str) {
		// TODO Auto-generated method stub
	
		
		char[] a=lstr.toCharArray();
		char[] b=str.toCharArray();
		int al=a.length;
		int bl=b.length;
		int i=0;
		int j=0;
		
		//获得next
		int [] next = new int[bl];
		next[0]=-1;
		int L=-1;
		int R=0;
		while(R<bl-1) {
			if(L==-1||b[L]==b[R]) {
				L++;
				R++;
				next[R]=L;
			}else {
				L=next[L];
			}
		}
		
		 
		
		
		while(i<al&&j<bl) {
			if(j==-1||a[i]==b[j]) {
				i++;
				j++;
			}
			else {
				j=next[j];
			}
		}
		if(j==bl) {
			return i-j; 
		}else {
			return 0;
		}

	}

}