28. Implement strStr()

題目原文

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().

解題思路

1. 學習如何使用substr()

程式解答

class Solution 
{
public:
    int strStr(string haystack, string needle) 
    {
        int strlen1 = haystack.length();
        int strlen2 = needle.length();
        int counter = strlen1 - strlen2 + 1;
        
        if (!strlen2)
            return 0;
        
        for (int i = 0; i < counter; i++)
            if (haystack.substr(i, strlen2) == needle)
                return i;
        
        return -1;
    }
};