class Solution {
public int strStr(String haystack, String needle) {
int n1 = haystack.length();
int n2 = needle.length();
int result=0;
if(n2 <=0)
return result;
for(int i =0;i<n1;i++){
if(haystack.charAt(i) == needle.charAt(0)){
result = i;
if(i+n2 > n1)
return -1;
if(haystack.substring(i,i+n2).equals(needle)){
return result;
}
}
}
return -1;
}
}
KMP
class Solution {
public int strStr(String haystack, String needle) {
int n = haystack.length(), m = needle.length();
if (m == 0) {
return 0;
}
int[] pi = new int[m];
for (int i = 1, j = 0; i < m; i++) {
while (j > 0 && needle.charAt(i) != needle.charAt(j)) {
j = pi[j - 1];
}
if (needle.charAt(i) == needle.charAt(j)) {
j++;
}
pi[i] = j;
}
for (int i = 0, j = 0; i < n; i++) {
while (j > 0 && haystack.charAt(i) != needle.charAt(j)) {
j = pi[j - 1];
}
if (haystack.charAt(i) == needle.charAt(j)) {
j++;
}
if (j == m) {
return i - m + 1;
}
}
return -1;
}
}