# 28. Find the Index of the First Occurrence in a String

題目：<https://leetcode.com/problems/find-the-index-of-the-first-occurrence-in-a-string/>

解法：直接解，找到第一個字元一樣之後，才比對後續字元，比對完正確則直接回傳 index

Python3：

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        lenH = len(haystack)
        lenN = len(needle)
        i = 0
        while (i < lenH - lenN + 1):
            if haystack[i] == needle[0]:
                j = 0
                k = i
                while (j < lenN):
                    if haystack[k] == needle[j]:
                        k += 1
                        j += 1
                    else:
                        break
                if j == lenN:
                    return i
            i += 1
        return -1

if __name__ == '__main__':
    haystack = "sadbutsad"
    needle = "sad"

    ans = Solution().strStr(haystack, needle)
    print(ans)

C：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int strStr(char * haystack, char * needle) {
    int lenH = strlen(haystack);
    int lenN = strlen(needle);
    for (int i = 0; i < lenH - lenN + 1; i++) {
        if (haystack[i] == needle[0]) {
            int j = 0, k = i;
            while (j < lenN) {
                if (haystack[k] == needle[j]) {
                    k++;
                    j++;
                } else
                    break;
            }
            if (j == lenN)
                return i;
        }
    }
    return -1;
}

int main() {
    char haystack[] = "sadbutsad";
    char needle[] = "sad";
    
    int ans = strStr(haystack, needle);
    printf("%d\n", ans);
    return 0;
}

###### tags: `leetcode` `string`