KMP算法（java）

来源：互联网发布：网球王子u17漫画软件编辑：程序博客网时间：2024/06/06 11:04

KMP算法是在字符串M中查找是否包含字符串N，存在返回字符串M匹配的字符首位置，将复杂度O(mn)降为O(m+n)

要看对KMP算法的理解，请参考字符串匹配的KMP算法

要看其中对匹配表的理解，请参考 KMP算法最浅显理解——一看就明白

下面是基于算法整理的Java代码：

public class KMP {private static int[] getNext(String b) {int len = b.length();int j = 0;int next[] = new int[len + 1];next[0] = next[1] = 0;for (int i = 1; i < len; i++) {while (j > 0 && b.charAt(i) != b.charAt(j)) {j = next[j];}if (b.charAt(i) == b.charAt(j)) {j++;}next[i + 1] = j;}return next;}public static List<Integer> search(String original, String find) {List<Integer> pos = new ArrayList<Integer>();int[] next = getNext(find);int j = 0;for (int i = 0; i < original.length(); i++) {while (j > 0 && original.charAt(i) != find.charAt(j))j = next[j];if (original.charAt(i) == find.charAt(j)) {j++;}if (j == find.length()) {pos.add(i - j + 1);j = 0;}}return pos;}public static int searchFirst(String original, String find) {int pos = -1;int[] next = getNext(find);int j = 0;for (int i = 0; i < original.length(); i++) {while (j > 0 && original.charAt(i) != find.charAt(j))j = next[j];if (original.charAt(i) == find.charAt(j)) {j++;}if (j == find.length()) {pos = i - j + 1;break;}}return pos;}public static void main(String[] args) {    String a = "abcaabababaa";    String b = "abaa";        //List<Integer> aaa = search(a, b);    int bbb = searchFirst(a, b);        //System.out.println(aaa);    System.out.println(bbb);    }}

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