0028. Find the Index of the First Occurrence in a String¶

package findtheindexofthefirstoccurrenceinastring

// 暴力解
// 時間複雜 O(M*N), 空間複雜 O()
func strStr(haystack string, needle string) int {
    haystackLen := len(haystack)
    needleLen := len(needle)
    index := 0
    for i := 0; i <= (haystackLen - needleLen); i++ {
        j := 0
        for j = 0; j < needleLen; j++ {
            if haystack[i+j] == needle[j] {
                index = i
            } else {
                break
            }
        }
        if j == needleLen {
            return index
        }
    }
    return -1
}

// Slice 解法
func strStrSlice(haystack string, needle string) int {
    haystackLen := len(haystack)
    needleLen := len(needle)
    if haystackLen == 0 || haystackLen < needleLen {
        return -1
    }
    if needleLen == 0 {
        return 0
    }
    for i := 0; i <= (haystackLen - needleLen); i++ {
        if haystack[i:i+needleLen] == needle {
            return i
        }
    }
    return -1
}