next:最长相等前后缀~~ 次长
class Solution {
public int strStr(String haystack, String needle) {
int n = haystack.length();
int m = needle.length();
if(m == 0){
return 0;
}
int[] next = new int[m];
for(int i = 1, j = 0; i < m; i++){
while(j > 0 && needle.charAt(i) != needle.charAt(j)){
j = next[j - 1];
}
if(needle.charAt(i) == needle.charAt(j)){
j++;
}
next[i] = j;
}
for(int i = 0, j = 0; i < n; i++){
while(j > 0 && haystack.charAt(i) != needle.charAt(j)){
j = next[j - 1];
}
if(haystack.charAt(i) == needle.charAt(j)){
j++;
}
if(j == m){
return i - m + 1;
}
}
return -1;
}
}