LeetCode-Implement strStr()

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

解答

开始写的代码竟然超时

public int strStr(String haystack, String needle) {
if (haystack == null || needle == null || haystack.length() < needle.length())
return -1;
if (needle.equals("")) {
return 0;
}
int i = 0, j = 0, index = -1, k;
while (i < haystack.length()) {
if (haystack.charAt(i) == needle.charAt(0)) {
index = i;
for (j = 0, k = i; j < needle.length() && k < needle.length(); j++, k++) {
if(haystack.charAt(k) != needle.charAt(j))
break;
}
}
if (j == needle.length()) {
return index;
}
i++;
}
return -1;
}

之后做了简单的优化，把最外层循环的迭代降低了，如下：

public int strStr(String haystack, String needle) {
if (haystack == null || needle == null || haystack.length() < needle.length())
return -1;
if (needle.equals("")) {
return 0;
}
int i = 0, j = 0, index = -1, k;
while (i < haystack.length()-needle.length()+1) {
if (haystack.charAt(i) == needle.charAt(0)) {
index = i;
for (j = 0, k = i; j < needle.length(); j++, k++) {
if(haystack.charAt(k) != needle.charAt(j))
break;
}
}
if (j == needle.length()) {
return index;
}
i++;
}
return -1;
}

这个竟然AC了，也是醉了。。。