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String matching

Certification: Basic Level Accuracy: 75% Submissions: 4 Points: 5

Write a Java program to implement the strStr() function, which finds the first occurrence of a substring (needle) in a string (haystack). Return the index of the first occurrence of the needle in the haystack, or -1 if the needle is not part of the haystack.

Example 1
     
  • Input: haystack = "hello", needle = "ll"
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  • Output: 2
    •  
  • Explanation: 
       
    • Step 1: We need to find the first occurrence of "ll" in "hello".
      •  
    • Step 2: Iterate through the haystack string, comparing substrings of length needle.length with the needle.
      •  
    • Step 3: At index 0, substring "he" doesn't match "ll".
      •  
    • Step 4: At index 1, substring "el" doesn't match "ll".
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    • Step 5: At index 2, substring "ll" matches the needle "ll".
      •  
    • Step 6: Return index 2 as the first occurrence.
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    •
Example 2
     
  • Input: haystack = "aaaaa", needle = "bba"
    •  
  • Output: -1
    •  
  • Explanation: 
       
    • Step 1: We need to find the first occurrence of "bba" in "aaaaa".
      •  
    • Step 2: Iterate through the haystack string, comparing substrings of length needle.length with the needle.
      •  
    • Step 3: Check substrings at indices 0, 1, and 2, all of which are "aaa".
      •  
    • Step 4: No substring matches "bba".
      •  
    • Step 5: Return -1 since the needle is not found in the haystack.
      •  
    •
Constraints
     
  • 0 ≤ haystack.length, needle.length ≤ 5 * 10^4
    •  
  • haystack and needle consist of only lowercase English characters
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  • Return 0 if needle is an empty string
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  • Time Complexity: O(n*m) where n is the length of haystack and m is the length of needle
    •  
  • Space Complexity: O(1)
    •
StringsCapgeminiSwiggy
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Hint
Solution

Solution Hints

    
  
  • Consider edge cases: empty needle should return 0, and if needle is longer than haystack, return -1
    • 
  
  • Use a sliding window approach to compare substrings of haystack with needle
    • 
  
  • Start from each position in haystack and check if the substring matches the needle
    • 
  
  • Optimize by breaking the comparison as soon as a mismatch is found
    • 
  
  • Consider using the KMP (Knuth-Morris-Pratt) algorithm for a more efficient solution if needed
    •

Steps to solve by this approach:

 Step 1: Handle edge cases - return 0 if needle is empty and -1 if needle is longer than haystack.
 Step 2: Iterate through haystack from index 0 to (haystackLength - needleLength).
 Step 3: For each starting position i in haystack, compare the substring starting at i with needle.
 Step 4: If a mismatch is found during comparison, break the inner loop and move to the next starting position.
 Step 5: If the entire needle matches a substring, return the starting index i.
 Step 6: If no match is found after checking all possible starting positions, return -1.
 Step 7: The output for the examples will be 2 and -1 respectively.

Submitted Code :