[LeetCode] 11.Implement strStr()

leetcode.com/problems/implement-strstr/

Implement strStr() - LeetCode

1. Problem

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.

2. Code

package leetCode;

public class ImplementStrstr {
	public static void main(String[] args) {
		String haystack = "mississippi";
		String needle = "pi";
		strStr(haystack, needle);
	}

	public static int strStr(String haystack, String needle) {
		if(needle.equals(0)) {
			return 0;
		}
        
		for(int i = 0; i < haystack.length() - needle.length() +1; i++) {
			boolean include = true;
			for(int j = 0; j < needle.length(); j++) {
				//System.out.println(haystack.charAt(i+j) + " " + needle.charAt(j));
				if(haystack.charAt(i+j) != needle.charAt(j)) { 
					include = false;
					break;
				}
			}
			if(include) {
				return i;
			}
		}
		return -1;
	}
}

 

3. Report

equals 메소드는 비교하고자 하는 대상의 내용 자체를 비교하지만, == 연산자는 비교하고자 하는 대상의 주소값을 비교합니다.

 

이 문제는 string.indexOf(string)을 구현하는 것과 같다

haystack.indexOf(needle)을 써도 제출이 가능하다 ㅎ