public int KMP(String s1, String s2) {
if(s2.length() == 0) return 0;
int i = 0,j = 0;
int[] next = getNext(s2);
while(i < s1.length() && j < s2.length()){
if(j == -1 || s1.charAt(i) == s2.charAt(j)){
i ++;
j ++;
}else{
j = next[j];
}
}
if(j == s2.length()) return i-j;
else return -1;
}
public int[] getNext(String s){
int[] next = new int[s.length()];
int j = 0,k = -1;
next[0] = -1;
while(j < s.length()-1){
if(k == -1 || s.charAt(j) == s.charAt(k)){
j ++;
k ++;
if(s.charAt(j) == s.charAt(k)) next[j] = next[k];
else next[j] = k;
}else{
k = next[k];
}
}
return next;
}