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First Occurrence of Substring

Certification: Basic Level Accuracy: 0% Submissions: 0 Points: 5

Write a C program to implement the strStr() function. Given two strings haystack and needle, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Note: For the purpose of this problem, when needle is an empty string, the function should return 0. This is consistent with C's strstr() and Java's indexOf().

Example 1
    
  
  • Input: haystack = "hello", needle = "ll"
    • 
  
  • Output: 2
    • 
  
  • Explanation:

    Step 1: Compare "he" with "ll". No match.

    Step 2: Compare "el" with "ll". No match.

    Step 3: Compare "ll" with "ll". Match found.

    Step 4: The starting index of the match is 2.
    •
Example 2
    
  
  • Input: haystack = "aaaaa", needle = "bba"
    • 
  
  • Output: -1
    • 
  
  • Explanation:

    Step 1: Compare "aaa" with "bba". No match.

    Step 2: Compare "aaa" with "bba". No match.

    Step 3: Compare "aa" with "bba". No match.

    Step 4: No match found in the entire haystack.

    Step 5: Return -1.
    •
Constraints
    
  
  • 0 ≤ haystack.length, needle.length ≤ 5 * 10^4
    • 
  
  • haystack and needle consist of only lowercase English characters
    • 
  
  • Time Complexity: O(n * m) for the naive approach, where n is the length of haystack and m is the length of needle
    • 
  
  • Space Complexity: O(1), constant extra space
    •
StringsAlgorithmsWalmartPhillips
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Hint
Solution

Solution Hints

    
  
  • Use the naive approach: check for the needle at each position of the haystack
    • 
  
  • Implement a more efficient algorithm like Knuth-Morris-Pratt (KMP) or Boyer-Moore
    • 
  
  • Use a sliding window approach to iterate through the haystack
    • 
  
  • For each position in the haystack, check if the substring starting at that position matches the needle
    • 
  
  • Take advantage of early termination when a mismatch is found
    •

Steps to solve by this approach:

 Step 1: Handle the special case where the needle is an empty string, return 0.

 Step 2: Calculate the lengths of both the haystack and needle strings.

 Step 3: If the needle is longer than the haystack, return -1 as it cannot be a substring.

 Step 4: Iterate through the haystack up to the position (haystack length - needle length).

 Step 5: For each position, compare the substring starting at that position with the needle.

 Step 6: If all characters match, return the starting index of the match.

 Step 7: If no match is found after checking all possible positions, return -1.

Submitted Code :