Leet me code 6 - [LeetCode][C++] 28. Implement strStr() (Easy)

leet me code!

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https://leetcode.com/problems/implement-strstr/

Implement strStr() - LeetCode

28. Implement strStr()

Implement strStr().

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

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().

 

Example 1:

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

Example 2:

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

Example 3:

Input: haystack = "", needle = ""
Output: 0

 

Constraints:

• 0 <= haystack.length, needle.length <= 5 * 104
• haystack and needle consist of only lower-case English characters.

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문제 정리

strStr() 구현하는 문제

주어진 단어 needle이 haystack에 포함된 경우, 처음 needle이 나타난 위치를 반환

haystack안에 포함되지 않은 경우 -1, needle이 empty인 경우 0 리턴

 

생각의 흐름

two pointer

haystack 한글자씩 needle과 비교

needle의 길이만큼 탐색이 된 경우(j == nsize), needle이 포함되었다고 판단하고 그때의 첫 위치 반환(i)

 

Solution 코드

class Solution {
public:
    int strStr(string haystack, string needle) {
        int hsize = haystack.size();
        int nsize = needle.size();
        
        int i = 0;
        while (i <= hsize-nsize) {
            int j = 0;
            while (j < nsize) {
                if (haystack[i+j] != needle[j]) break;
                j++;
            }
            if (j == nsize) return i;
            i++;
        }
        
        return -1;
    }
};