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kmp.java
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108 lines (93 loc) · 3.02 KB
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package BasicSortSolution.string;
import java.util.Random;
/**
* Created by gump on 2017/4/21.
*/
public class kmp {
public static Random random = new Random();
public static String randomStr(){
StringBuilder sb = new StringBuilder();
int i = 100;
while (i-- >0){
sb.append((char)('a'+random.nextInt(26)));
}
return sb.toString();
}
public static void main(String argc[]){
System.out.println("Comparing trad str comparsion alg with kmp...");
String tar = randomStr();
int randomStart = random.nextInt(tar.length()-10);
String pattern = tar.substring(randomStart,randomStart+10);
System.out.printf("text:%s\npattern:%s\n",tar,pattern);
System.out.printf("Start point:%d\n",randomStart);
System.out.println();
long beforeTradStart = System.currentTimeMillis();
boolean result = trad(tar,pattern);
long tradStartend = System.currentTimeMillis();
System.out.printf("result:%b\ttrad comparsion cost:%d\n",result,tradStartend-beforeTradStart);
long beforeKMPStart = System.currentTimeMillis();
boolean KMPresult = KMP(tar,pattern);
long KMPStartend = System.currentTimeMillis();
System.out.printf("result:%b\tkmp comparsion cost:%d\n",KMPresult,KMPStartend-beforeKMPStart);
}
private static boolean KMP(String tar, String pattern) {
int next[] = new int[pattern.length()];
int i=1,j=0;
while (i<pattern.length()){
if(pattern.charAt(i) == pattern.charAt(j)){
next[i] = j+1;
i++;j++;
}else {
if(j==0){
i++;
continue;
}
while (pattern.charAt(i) != pattern.charAt(j)
&& j!=0){
j = next[j-1];
}
if(pattern.charAt(i) == pattern.charAt(j)){
next[i] = j+1;
j++;i++;
}else{
i++;
}
}
}
i=0;
while (j<pattern.length() &&i<tar.length()){
if(tar.charAt(i) == pattern.charAt(j)){
i++;j++;
continue;
}else{
if(j==0){
i++;continue;
}else{
j=next[j-1];
}
}
}
if(j>=pattern.length()){
return true;
}
return false;
}
private static boolean trad(String tar, String pattern) {
int i = 0;
while (i<tar.length()){
int temp = i;
for (int j = 0; j < pattern.length(); j++) {
if(tar.charAt(temp) == pattern.charAt(j)) {
temp++;
}else{
break;
}
}
if((temp-i)==pattern.length()){
return true;
}
i++;
}
return false;
}
}