C语言 | Leetcode C语言题解之第28题找出字符串中第一个匹配项的下标

题目：

题解：

int strStr(char* haystack, char* needle) {int n = strlen(haystack), m = strlen(needle);if (m == 0) {return 0;}int pi[m];pi[0] = 0;for (int i = 1, j = 0; i < m; i++) {while (j > 0 && needle[i] != needle[j]) {j = pi[j - 1];}if (needle[i] == needle[j]) {j++;}pi[i] = j;}for (int i = 0, j = 0; i < n; i++) {while (j > 0 && haystack[i] != needle[j]) {j = pi[j - 1];}if (haystack[i] == needle[j]) {j++;}if (j == m) {return i - m + 1;}}return -1;
}