Php Program To Check If A String Is Substring Of Another
Given two strings s1 and s2, find if s1 is a substring of s2. If yes, return the index of the first occurrence, else return -1.
Input: s1 = "for", s2 = "geeksforgeeks" Output: 5 Explanation: String "for" is present as a substring of s2. Input: s1 = "practice", s2 = "geeksforgeeks" Output: -1. Explanation: There is no occurrence of "practice" in "geeksforgeeks"
Simple Approach: The idea is to run a loop from start to end and for every index in the given string check whether the sub-string can be formed from that index. This can be done by running a nested loop traversing the given string and in that loop run another loop checking for sub-string from every index.
For example, consider there to be a string of length N and a substring of length M. Then run a nested loop, where the outer loop runs from 0 to (N-M) and the inner loop from 0 to M. For very index check if the sub-string traversed by the inner loop is the given sub-string or not.
Present at index 5
- Time complexity: O(m * n) where m and n are lengths of s1 and s2 respectively.
A nested loop is used the outer loop runs from 0 to N-M and inner loop from 0 to M so the complexity is O(m*n).
- Space Complexity: O(1).
As no extra space is required.