[LeetCode] 28. 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

public class ImplementStrStr {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int result = strStr("hello", "lo");
		System.out.println(result);
	}

    public static int strStr(String haystack, String needle) {
    	if(needle.equals(" "))
    		return 0;
        return haystack.indexOf(needle);
    }
}

 

3. Report

 String Class의 indexOf 메소드를 이용해서 문제 해결했다.

 

indexOf의 소스코드는 아래와 같다.

	public int indexOf(int var1, int var2) {
		int var3 = this.value.length;
		if (var2 < 0) {
			var2 = 0;
		} else if (var2 >= var3) {
			return -1;
		}

		if (var1 < 65536) {
			char[] var4 = this.value;

			for (int var5 = var2; var5 < var3; ++var5) {
				if (var4[var5] == var1) {
					return var5;
				}
			}

			return -1;
		} else {
			return this.indexOfSupplementary(var1, var2);
		}
	}

	private int indexOfSupplementary(int var1, int var2) {
		if (Character.isValidCodePoint(var1)) {
			char[] var3 = this.value;
			char var4 = Character.highSurrogate(var1);
			char var5 = Character.lowSurrogate(var1);
			int var6 = var3.length - 1;

			for (int var7 = var2; var7 < var6; ++var7) {
				if (var3[var7] == var4 && var3[var7 + 1] == var5) {
					return var7;
				}
			}
		}

		return -1;
	}

자바의 java.lang라이브러리 jar파일을 디컴파일한 결과 난독화 되어있어서 변수명을 읽기가 어려웠다.