KMP
KMP.java 源码
package algorithm.string;
/**
* @author roseduan
* @time 2019/7/8 11:34
* @description KMP算法实现
*/
public class KMP {
public static int knuthMorrisPratt(String main, String ptn) {
int n = main.length();
int m = ptn.length();
if (n == 0 || m == 0 || m > n){
return -1;
}
int[] next = getNext(ptn, m);
int j = 0;
for (int i = 0; i < n; i ++) {
//说明有好前缀
while (j > 0 && main.charAt(i) != ptn.charAt(j)){
j = next[j - 1] + 1;
}
if (main.charAt(i) == ptn.charAt(j)){
++ j;
}
if (j == m){
return i - m + 1;
}
}
return -1;
}
/**
* 失效函数计算方法
*/
private static int[] getNext(String ptn, int m) {
int[] next = new int[m];
next[0] = -1;
int k = -1;
for (int i = 1; i < m; i ++) {
while (k != -1 && ptn.charAt(k + 1) != ptn.charAt(i)){
k = next[k];
}
if (ptn.charAt(k + 1) == ptn.charAt(i)){
++ k;
}
next[i] = k;
}
return next;
}
}
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