数据结构与算法

KMP算法

 public static void main(String[] args) {
        String s1 = "15846548 565";
        String s2 = "548";
        int[] next = kmpNext(s2);
        int index=kmpSearch(s1,s2,next);
        System.out.println(index);
    }

    //Kmp匹配
    public static int kmpSearch(String str1, String str2, int[] next) {
        //遍历
        for (int i = 0, j = 0; i < str1.length(); i++) {
            while (j > 0 && str1.charAt(i) != str2.charAt(j)) {
                j = next[j - 1];
            }
            if (str1.charAt(i) == str2.charAt(j)) {
                j++;
            }
            if (j == str2.length()) {//匹配成功
                return i - j + 1;//因为str1.charAt(i)==str2.charAt(j)时j加一了
            }
        }
        return -1;
    }


    //获取子串的部分匹配值表
    public static int[] kmpNext(String dest) {
        //创建一个next数组保存部分匹配值
        int[] next = new int[dest.length()];
        next[0] = 0;
        for (int i = 1, j = 0; i < dest.length(); i++) {
            //当dest.charAt(i)==dest.charAt(j)满足时，匹配值加一
            if (dest.charAt(i) == dest.charAt(j)) {
                j++;
            }

            //当dest.charAt(i)!=dest.charAt(j)时，需要从next[j-1]获取新的j
            //直到dest.charAt(i)==dest.charAt(j)成立才退出
            while (j > 0 && dest.charAt(i) != dest.charAt(j)) {
                j = next[j - 1];
            }
            next[i] = j;
        }
        return next;
    }