KMP-next-nextval

  1 package com.kk.string;
  2 
  3 public class Main {
  4 
  5     /**
  6      * @param args
  7      */
  8     public static void main(String[] args) {
  9     char[] s = "要深入理解和精準把握黨的十九大精神，結合實際紮紮實實貫徹黨的十九大決策部署，緊扣中國特點社會主義新時代的新要求，推進黨和國家各項事業不斷邁上新臺階".toCharArray();
 10     char[] t = "新臺階".toCharArray();
 11     System.out.println(Main.index1(s, t, 0));
 12     System.out.println(Main.indexKMP(s, t, 0));
 13 
 14     }
 15 
 16     /**
 17      * 字符串的普通匹配算法
 18      * 
 19      * @param s
 20      * @param t
 21      * @param pos
 22      * @return
 23      */
 24     public static int index1(char[] s, char[] t, int pos) {
 25     int i = pos;
 26     int j = 0;
 27     while (i < s.length && j < t.length) {
 28         if (s[i] == t[j]) {
 29         i++;
 30         j++;
 31         } else {
 32         i = i - j + 1;
 33         j = 0;
 34         }
 35     }
 36     if (j == t.length)
 37         return i - j;
 38     else
 39         return -1;
 40     }
 41 
 42     /**
 43      * 首尾匹配算法
 44      * 
 45      * @param s
 46      * @param t
 47      * @param pos
 48      * @return
 49      */
 50     public static int index2(char[] s, char[] t, int pos) {
 51     // int i = pos;
 52     // int j = 0;
 53     return -1;
 54     }
 55 
 56     /**
 57      * KMP算法
 58      * 
 59      * @param s
 60      * @param t
 61      * @param pos
 62      * @return
 63      */
 64     public static int indexKMP(char[] s, char[] t, int pos) {
 65     int[] next = Main.getNextval(t);
 66     int i = pos;
 67     int j = 0;
 68     while (i < s.length && j < t.length) {
 69         if (j == -1 || s[i] == t[j]) {
 70         j++;
 71         i++;
 72         } else {
 73         j = next[j];
 74         }
 75     }
 76     if (j == t.length)
 77         return i - j;
 78     else
 79         return -1;
 80     }
 81 
 82     /**
 83      * getNext
 84      * 
 85      * @param t
 86      * @param next
 87      */
 88     public static int[] getNext(char[] t) {
 89     if (null == t || t.length == 0)
 90         return null;
 91     //
 92     int[] next = new int[t.length];
 93     int j = 0;
 94     int i = 0;
 95     next[0] = -1;
 96     while (i < t.length) {
 97         if (j == 0 || t[i] == t[j]) {
 98         next[i] = j - 1;
 99         i++;
100         j++;
101         } else {
102         j = next[j];
103         }
104     }
105     return next;
106     }
107 
108     /**
109      * getNextval
110      * 
111      * @param t
112      * @param next
113      */
114     public static int[] getNextval(char[] t) {
115     if (null == t || t.length == 0)
116         return null;
117     //
118     int[] nextval = new int[t.length];
119     int j = 0;
120     int i = 0;
121     nextval[0] = -1;
122     while (i < t.length) {
123         if (j == 0 || t[i] == t[j]) {
124         if (t[i] != t[j]) {
125             nextval[i] = j - 1;
126         } else {
127             nextval[i] = nextval[j];
128         }
129         i++;
130         j++;
131         } else {
132         j = nextval[j];
133         }
134     }
135     return nextval;
136     }
137 
138 }