# Why my KMP algorithm (13ms) is slow than Brute Force (8ms)

• public class Solution {
public int strStr(String haystack, String needle) {
if (haystack == null || needle == null || haystack.length() < needle.length()) return -1;
if (needle.length() == 0) return 0;
int[] lps = preprocess(needle);
int i = 0;
int j = 0;
while (i < haystack.length()) {
if (haystack.charAt(i) == needle.charAt(j)) {
if (j == needle.length() - 1) {
return i - j;
}
i++;
j++;
} else {
if (j > 0) {
j = lps[j - 1];
} else {
i++;
}
}
}
return -1;
}

public static int[] preprocess(String needle) {
if (needle == null || needle.length() == 0) return null;
int[] lps = new int[needle.length()];
if (needle.length() == 1) {
return lps;
}
int i = 1;
int j = 0;
while (i < lps.length) {
if (needle.charAt(i) == needle.charAt(j)) {
lps[i] = j + 1;
i++;
j++;
} else {
if (j > 0) {
j = lps[j - 1];
} else {
i++;
}
}
}
return lps;
}
}

Brute Force

public class Solution {
public int strStr(String haystack, String needle) {
if (haystack == null || needle == null || needle.length() < 1) return 0;
for (int i = 0; i < haystack.length(); i++) {
if (i + needle.length() > haystack.length()) return -1;
int m = i;
for (int j = 0; j < needle.length(); j++) {
if (needle.charAt(j) != haystack.charAt(m)) {
break;
} else {
if (j == needle.length() - 1) {
return i;
}
m++;
}
}
}
return -1;
}
}

• same here. :<

Maybe it's the test case is not well-designed?

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