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Longest Common Prefix

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

Write a C program to find the longest common prefix string amongst an array of strings. If there is no common prefix, return an empty string "".

A common prefix is a substring that occurs at the beginning of all strings in the array. The program should return the longest such substring.

Example 1
    
  
  • Input: strs = ["flower", "flow", "flight"]
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  • Output: "fl"
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  • Explanation:

    Step 1: Compare the first characters of all strings: 'f' is common.

    Step 2: Compare the second characters of all strings: 'l' is common.

    Step 3: Compare the third characters: 'o' in "flower" and "flow", but 'i' in "flight". Not common.

    Step 4: The longest common prefix is "fl".
    •
Example 2
    
  
  • Input: strs = ["dog", "racecar", "car"]
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  • Output: ""
    • 
  
  • Explanation:

    Step 1: Compare the first characters: 'd' in "dog", 'r' in "racecar", and 'c' in "car". Not common.

    Step 2: Since the first characters are different, there is no common prefix.

    Step 3: Return an empty string.
    •
Constraints
    
  
  • 1 ≤ strs.length ≤ 200
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  • 0 ≤ strs[i].length ≤ 200
    • 
  
  • strs[i] consists of only lowercase English letters
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  • Time Complexity: O(S), where S is the sum of all characters in all strings
    • 
  
  • Space Complexity: O(1), constant extra space
    •
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Hint
Solution

Solution Hints

    
  
  • Use a horizontal scanning approach: compare the first string with each of the other strings
    • 
  
  • Alternatively, use a vertical scanning approach: compare characters at the same position for all strings
    • 
  
  • You could also use a divide and conquer approach: find the common prefix of two halves recursively
    • 
  
  • Sort the array first to reduce the problem to finding the common prefix of just the first and last strings
    • 
  
  • Use binary search on the length of the prefix
    •

Steps to solve by this approach:

 Step 1: If the array is empty, return an empty string.

 Step 2: Take the first string as the initial prefix.

 Step 3: Iterate through the rest of the strings in the array.

 Step 4: For each string, compare it with the current prefix character by character.

 Step 5: If a mismatch is found, update the prefix length to the position where the mismatch occurred.

 Step 6: If the prefix becomes empty at any point, return an empty string.

 Step 7: After comparing with all strings, return the substring of the first string up to the updated prefix length.

Submitted Code :