Implement strStr() - String - Easy - LeetCode

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().

using System;
using System.Collections.Generic;
using System.Text;

namespace LeetCode.AskGif.Easy.String
{
 public class StrStrSoln
 {
 public int StrStr(string haystack, string needle)
 {
 if(haystack == needle)
 {
 return 0;
 }

 if (string.IsNullOrEmpty(haystack))
 {
 return -1;
 }

 if (string.IsNullOrEmpty(needle))
 {
 return 0;
 }

 if(needle.Length > haystack.Length)
 {
 return -1;
 }

 for(int i = 0; i < haystack.Length - needle.Length + 1; i++)
 {
 bool found = true;
 if (haystack[i] == needle[0])
 {
 for (int j = 1; j < needle.Length; j++)
 {
 if(haystack[i+j] != needle[j])
 {
 found = false;
 }
 }

 if (found)
 {
 return i;
 }
 }
 }
 return -1;
 }
 }
}

Time Complexity: O(n*m) where n is the length of haystack and m is the length of the needle.

Space Complexity: O(1)

Unit Tests:

using LeetCode.AskGif.Easy.String;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.String
{
 [TestClass]
 public class StrStrSolnTests
 {
 [TestMethod]
 public void StrStrSoln_First()
 {
 var haystack = "hello";
 var needle = "ll";
 var output = 2;
 var res = new StrStrSoln().StrStr(haystack, needle);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void StrStrSoln_Second()
 {
 var haystack = "aaaaa";
 var needle = "bba";
 var output = -1;
 var res = new StrStrSoln().StrStr(haystack, needle);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void StrStrSoln_Third()
 { 
 var haystack = "mississippi";
 var needle = "pi";
 var output = 9;
 var res = new StrStrSoln().StrStr(haystack, needle);

 Assert.AreEqual(res, output);
 }
 }
}