字符串匹配---KMP-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_61185410/article/details/123669355

本文介绍了一种字符串处理算法——Knuth-Morris-Pratt (KMP) 算法，用于在两个字符串中高效查找子串。通过实例展示了如何在Java中实现KMP算法，并提供了一个交互式输入验证。

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import javax.sound.sampled.EnumControl;
import java.sql.Array;
import java.util.*;
// 1:无需package
// 2: 类名必须Main, 不可修改

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String strA = input.nextLine();
        String strB = input.nextLine();
        int res = kmp(strA,strB);
        System.out.println(res);
    }
    public static int kmp(String strA,String strB){
        if(strA.length() == 0 || strB.length() == 0)return -1;
        if(strA.length()<strB.length())return -1;
        int[] next = next(strB);
        //System.out.println(Arrays.toString(next));
        int i = 0,j = 0;
        while(i<strA.length()){
            //System.out.print(strA.charAt(i)+" "+j+"\n");
            if(j == -1 || strA.charAt(i) == strB.charAt(j)){
                i++;j++;
            }
            else{
                j = next[j];
            }
            if(j==strB.length()){
                return i-j;
            }
        }
        return -1;
    }
    public static int[] next(String str){
        int[] res = new int[str.length()];
        res[0] = -1;
        if(str.length() ==1){
            return res;
        }
        char[] cArr = str.toCharArray();
        res[1] = 0;
        int j = 1;
        int k = res[j];

        while(j<str.length()-1){
            if(k<0 || cArr[j] == cArr[k]){
                res[++j] = ++k;
            }
            else{
                k = res[k];
            }
        }
        return res;
    }
}