Leetcode#28 Implement strStr()

 1 int strStr(char *haystack, char *needle) {
 2   if (!needle[0]) return 0;
 3   int n = strlen(needle);
 4   int *next = new int[n + 1];
 5   int i, j;
 6 
 7   i = 0;
 8   j = -1;
 9   next[0] = -1;
10   while (needle[i]) {
11     if (j < 0 || needle[i] == needle[j]) {
12       i++;
13       j++;
14       next[i] = j;
15     }
16     else
17       j = next[j];
18   }
19 
20   i = 0;
21   j = 0;
22   while (haystack[i] && j < n) {
23     if (j < 0 || haystack[i] == needle[j]) {
24       i++;
25       j++;
26     }
27     else
28       j = next[j];
29   }
30 
31   return j == n ? i - n : -1;
32 }