[LeetCode 解題報告]028. Implement strStr()

Implement strStr().

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

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Clarification:

What should we return when needle is an empty string? This is a great question to ask during an interview.

For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

考察：字符串查找子串，類似於string類的find()函數，複雜點的可以用字符串匹配kmp；

class Solution {
public:
    int strStr(string haystack, string needle) {
        if(needle == "")
            return 0;
        //return haystack.find(needle);
        int m = haystack.length(), n = needle.length();
        if (m < n)
            return -1;
        
        for (int i = 0; i <= m-n; i ++) {
            int j = 0;
            for (j = 0; j < n; j ++)
                if (haystack[i+j] != needle[j])
                    break;
            if (j == n)
                return i;
        }
        return -1;
    }
};